Power Problem - can't bootup - sometimes

RE: IBM Model 2170-245 with Windows 98. I was given this computer a couple years ago and it has run fine until a few months back when one day it would not come on. It was 100% dead. I removed the case to check the wires and when I barely touched the wires leading to the switch, they both came loose from the switch. I stripped the wire ends and could start the PC by touching the wires together. This worked ok for a few weeks, then it was dead again. Just wouldn't come on. It sat for a few days and when I touched the wires, the PC started. This time, when I finished, I put it in standby mode instead of shutting it down. This worked for a couple months, then during a storm the power went off for several hours. I held my breath as I touched the wires together and was surprised when the computer started ok. I thought I'd trying shutting it down when I finished with it and hoped it would start next time, and it did. I shut it down and it started when I touched the wires together each time for a couple weeks or so. It worked fine just last night. This afternoon when I touched the wires together, nothing happened. Dead again. There's no way to know if it will restart again, as it did before. More than a month ago a computer shop told me it's probably the power supply, but if that's true why would it come on sometimes and not others, and how could it stay in standby mode if the power supply is bad? I asked if the power supply could be tested and was told no, the only way to know if it's bad is to replace it. Someone else told me that's not true, that there is a fairly easy way to test the power supply and he is going to send me instructions, someday. Which is true? Can the power supply be tested and if so is there a simple way to do it? Do you think this is a power supply problem? If so, how could I tell if a power supply from another computer would work in this IBM? I have several computers around that have power supplies. The computer shop mentioned said there is no OEM parts available, that I'd have to get an aftrermarket power supply, so what would I look for? Is there any way to get the information off my hard drive? Would I have to use another IBM with W 98, or would the drive work on any PC with W 98? Most of the information is backed up to disks, but there are a few things I'd like to get. The computer shop said they can do it, but I was wondering how it's done. Do they have special equipment?

I asked if the power supply could be tested and was told no, the only way to know if it's bad is to replace it. Someone else told me that's not true, that there is a fairly easy way to test the power supply and he is going to send me instructions, someday.

Which is true? Can the power supply be tested and if so is there a simple way to do it?

Power supplies certainly can be tested, though it is very difficult for normal users to test conclusively so swapping in a known good PSU is typically the best way to verify if yours is good, or not. But to answer your questions, here is my canned text on testing PSUs:

To properly and conclusively test a power supply unit (PSU), it must be tested under various realistic "loads" then analyzed for excessive ripple and other anomalies. This is done by a qualified technician using an oscilloscope or power analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronic repair facilities.

Fortunately, there are other options that are almost as good. I keep a PSU Tester in my tool bag when I am "in the field" and don't have a good spare power supply to swap in. While not a certain test, they are better than nothing. The advantage of this model is that it has an LCD readout of the voltage. With an actual voltage readout, you have a better chance of detecting a "failing" PSU, or one barely within specified ATX Form Factor Standard tolerances. Lesser models use LEDs to indicate the voltage is just within some "range". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed". Newegg has several testers to choose from. All these testers contain a "dummy load" to fool the PSU into thinking it is connected to a motherboard, and therefore allows the PSU to power on, if able, without being attached to a motherboard - great for testing fans, but again, it is not a true load or suitable for conclusive testing.

Note the required voltage tolerance ranges:

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Swapping in a known good supply is a tried and true method of troubleshooting used for years, even by pros. If you have access to a suitably sized, spare power supply, carefully remove the suspect supply and replace it with the known good one, and see if the problem goes away.

I do not recommend using a multimeter to test power supplies. To do it properly, that is, under a realistic load, the voltages on all the pins must be measured while the PSU is attached to the motherboard and the computer powered on. This requires poking (with some considerable force) two hard and sharp, highly conductive meter probes into the main power connector, deep in the heart of the computer. One tiny slip can destroy the motherboard, and everything plugged into it. It is not worth the risk considering most multimeters, like plug-in testers, do not measure, or reveal any unwanted and potentially disruptive AC components to the DC voltages.

Note the ATX Form Factor standard does not "require" specific color coding for power supply connector wiring. It has recommendations but manufacturers often do not follow them. Sadly, many testing guides or tutorials will refer to wire color only and that can lead to improper testing.

The voltages can be checked in the BIOS Setup Menus of most motherboards but they do not reveal ripple or other anomalies either. And of course, booting into the BIOS Setup Menu requires a working PSU.

As always, before working in the interior of the computer case, take necessary ESD precautions to ensure static buildup in your body does not discharge through and destroy any sensitive devices. Unplug from the wall and touch bare metal of the case before reaching in. And remember, anything that plugs into the wall can kill. Do not open the power supply's case unless you are a qualified electronics technician. There are NO user-serviceable parts inside a power supply. If you do not have a tester or a suitable spare to swap in, take the PSU to a qualified technician for testing.

For more information on testing PSUs, see this excellent article by Gabriel Torres, Why 99% of Power Supply Reviews are Wrong.

Does the problem I discribed sound like a bad power supply? Last night I touched the two wires from the switch together a couple dozen times and nothing happened, so I gave up. This morning I tried again. First time I touched the wires together the computer started up just fine. It's in standby mode now. If the power supply is bad, would the computer come on?

Does the problem I discribed sound like a bad power supply?

It sounds like that is a good place to start. Unfortunately, there is no simple troubleshooting method to quickly pinpoint the fault. So typically you discover the fault through a process of eliminating possibilities.

Also, since a power supply must provide 3 voltages (+12VDC, +5VDC, and +3.3VDC) a problem with any can result in problems.