System becomes non-responsive

An elderly couple that I am friends with asked me to look at their PC as it had started behaving badly. When they asked me to look at it, it would display nothing on the monitor upon booting – just a black screen – and the monitor indicator light gave no indication that the system was even attempting to communicate with the monitor. Prior to that, they had been having trouble where suddenly the "mouse would stop working"; and according to them the only way out was to hard-boot the machine. I agreed to take it home with me and take a look, and see if I could diagnose what was going on. I figured if the video interface on the motheboard had failed I could put a PCI video card in for $20 or so. The first thing I found when I got it home and opened the case was 5 or 6 years of accumulated dust. So I took the machine outside with a couple of cans of compressed air, and gave it a good cleaning. Then I hooked it up to a monitor and keyboard I had laying around and voila!, the machine booted and everything was visible on the screen as it should be. However, after a very few minutes, the mouse quit responding, and the keyboard also would not respond – CTRL-ALT-DEL did nothing. And, as they had told me, the only way I could get out was to hard-boot the machine. Over the course of the last couple of days, I have tried a number of things with no success. On one occasion, I managed to get Process Explorer running, and observed that when the machine locked up the CPU utilization was only about 65% and memory utilization was about 80%. I booted into Safe Mode and found that the system still locked up – sometimes even before the boot process finished. They had told me there was nothing on the machine of any importance. The only thing they use if for is to play games (so I had a suspicion around the existence of malware — but I never did get to run HJT or MAB all the way through without the system hanging); and to use Facebook and email to stay in touch with family around the country. So, they had told me to delete anything I felt needed to be deleted. Therefore, last night I decided to go back to factory settings and start over; using CTRL-F11 to access the hidden partition and reinstall Windows-XP. The initial software load went okay – and I am now sitting at a user set-up prompt with the system apparently hung, again (in any event, the cursor doesn't move with the mouse and CTRL-ALT-DEL on the keyboard does nothing). The conclusion that I have come to is that I'm dealing with a hardware problem, and the computer might not even be salvagable. But, before I completely give up on it I thought I would see if anybody more knowledgable than me has any ideas. I would appreciate any suggestions that anyone might have.

I tend to agree with what you have surmised, but lets see what we can prove before going to a new system, to begin with if video was\is on the way out, it would not be a wise investment to add a further card, because if the board is going, who knows what else may be about to go, so this is usually the time one would consider a complete upgrade.

Now infection is still possible, face book users are often targeted, what I suggest is to try running scans at boot, A Squared has a version to put on a thumb drive, give that a try booting to it and scanning, also the UBCD has some scans available on it, try booting to that and run a few of those scans in the anti virus section of the files, also try a scan with Stinger, the hope is if this is an infection issue, or at least is being hampered by an infection, such tools will remove enough to allow you access to the system so you can run further scans, also if you are able to install Avast, update it then tell it run a scan at boot, it used to ask during install if you wished to do this, not sure if it still does though.

The hardware can be seriously affected by dust, and from what you said it wouldn't surprise me if there is\was an over heating issue, possibly damage accumulated over the years perhaps, but the motherboard is probably the hardest piece of hardware to prove faulty, all you can do is check everything else so nothing more is left, then it's a leap of faith, so begin by entering the bios, see if there is a system health section, or whatever that board may call it, but see if you can see any temperature read outs for the CPU, anything over 60 (generally speaking) means it needs the heatsink re-seating, over 70 and it's going to cause damage, well you start entering that area anyway, although there may be odd exceptions, but nearly all systems I touch are around 30 or better as a guide.

Do you have a PSU tester ?
You can get them pretty cheap these days, and it will help show if the power is OK or not, if this is bad then you could be damaging the system using it, also not sure what age it is, but it may be worth trying another CMOS battery, when they start to go you can get some real funkiness going on lol, to get an idea check the time\date in the bios when checking for system health, if this is out then it's probably time for it to be replaced.

Also when using the UBCD (assuming you do) run the memory check, this will see if the ram may be starting to fail, also run the hard drive makers scan, the UBCD has them all, just identify which make is the drive in the system, then use they're utility to scan the hard drive, use the extended scan, this will check the hard drive for bad sectors etc, at least with these scans they can prove those items one way or the other, therefore giving you an answer to an issue, or ruling them out of the equation, thus leaving a shorter list of suspects, see how you go with this, and we can go from there.