system shut down at some randon time automatically :( WHY ??

[mileytipton]

hi,
I am a computer user, with least knowledge of its internal system and working. My system generally shuts down automatically at some random time, (like a ghost doing this). I scan my system twice and thrice but there is no virus problem..
What are probable reason behind it ... ??
And what can I do in this case.. ?

[excellentlab]

HI DEAR
YOUR SYSTEM FILE LSASS.EXE IS CRPT.
OR SESSOR VIRUSE.KINDLY RE INSTAL WINDOWS

[torbjorn]

When the system shuts down by itself, does the operating system take itself down properly or is it just a "raw" power off? In the latter case, it is probably a hardware problem - for example, overheating due to a faulty fan or coolers clogged with dust. Also, bad electrolytic capacitors in the power supply or on the motherboard could be to blame.

NEVER try to solve strange problems by reinstalling the operating system. In the long run, it is a much better approach to study and understand the problem and then fix the root cause. You will save a lot of time as compared to the time of reinstalling the operating system and then perform software installations and configurations to get the computer to behave as you want.