there could be many thing:
software wise (OS, application, malware, etc)
Hardware wise (heat, cold, dust, electricity, dust, etc)

to see if it is indee hardware:
go to bios, check the...

it is china made, about 2-3 dollars worth. not strong but enough for cards and keyboard cleaning...
there also a small compressor (you can wrap your hand around it) about 5-7 dollars worth, but must...

yes you are right, using compressor is the best one...
i guess i'm too used to mine using special vacuum, it's small one using usb as its source of power, it is not generating heat, so it is ok for...

yes you need to open the cpu casing to see whether it is full of dust or not. because sometimes dust can make your hardware behavior strangely.
to clean the dust, take off all component except the...

try slaving your hdd to another computer and scan it to see if it really is because of virus.
while you wait for the scan result, try to boot up you pc to see if it can stay up long, better if you...

i've experiencing the same problem with the installer trying to install visual foxpro,
i basically insert the installation cd, and reinstall the software and uninstall it again with several times...

have you tried seeing the power dc output in bios, see if the dc output is fluctuated so much. if so then you need an ups to stabilize your electricity...
otherwise you look up for the...

have you considered the dust?