Hi Temujin,
Its good to know that your computer is free of viruses and other malicious code.
1 It would be wise to identify if its a hardware problem with your computer or a software or operating system issue, so as a first step please download a live distro of Linux ( Puppy is good) burn the .iso as an image (make sure its a burnt as an image as a copy will not work.)
2 Boot your computer from the Puppy disc you have just burnt (don't install Puppy. just let it run in RAM) and with your Ethernet cable connected (for Internet access) give your computer a good workout and see if after several hours of use the problems are cured or if they remain.
3 If the problems continue exactly the same as when running under Windows then we have probably identified that a hardware issue is at the root of the problems you have been experiencing.
4 If the computer runs well under Puppy Linux (make allowances for the fact that it will be running entirely within RAM) then it is pointing towards Windows or software as the likely culprit.
5 I will shortly be leaving for my holiday so I will set out the logic tree that could be used to help diagnose and solve the issues….. Post back if you require detailed directions on how to proceed and one of the Techs on the forum here will provide them or I will do so as soon as I return (around 2 weeks time or so)
6 If its likely a hardware issue then starting at the wall socket check the output voltage and frequency matches that required for your machine, next check the Ram modules by removing and refitting (to remove any oxidation of the contacts) If you have multiple memory modules check them by using just one or two in isolation and then thoroughtly testing how the computer performs on say half RAM) Next check the Power Supply Unit for correct output on all rails..(this is not easy to do without the correct test equipment that provides the correct "load" to the system, so if in any doubt just replace with a compatible PSU for testing purposes and give it extensive use to see how it runs) Next plug in a motherboard tester and compare the digital output with the mobo testers handbook to see if any problems are identified
7 If on the other hand the computer works well under Puppy Linux then boot into Windows safe mode with networking and test thoroughly….. ( Warning your anti virus and other protections will not be working properly during this test so be careful!) if things are Ok (computer works well) using this approach then its likely some thing that is loading with normal Windows but not in safe mode is a likely candidate for suspicion and MSCONFIG can be used to help identify the problem.
8 If running under safe mode with networking offers no relief to the problem then set up a new admin level account (Control Panel >User accounts) and reboot the machine and log into the new account that you have just created ( carry out a good test using this new account…..) is this operating any better?
9 Temperature testing, Hard drive, CPU, RAM can also be tested by downloading the appropriate utilities (burn them to disc etc)….
10 Hopefully the above will set you on the right road but I need to issue a warning:
Because you built your machine yourself, hopefully you took all the required ESD (anti static) and personal safety requirements…… there are lethal voltages involved so using an incorrect proceedure or carrying it out incorrectly can have catastrophic results and lead to death or serious injury, not to mention damage to your computer and or loss of data, so if in any doubt take it to a competent computer technician or a repair shop of good reputation.
Post back if you need further information, but as a priority I recommend you check your back up strategy has worked effectively and everything that is important to you on your machine is comprehensively backed up, 100% accurate, reproducible and with at least one extra copy kept safe offsite on removable media… If your disc images are not up to date then make a complete disc image now of your hard drive and ensure you have a method of booting your computer and accessing the image in the event that your machine is no longer able to boot into Windows.
Regards
paws