PLS HELP!!! pc windows freezing?

No virus-malware,trojan threats,well scanned,defragmented as Comodo full scan suggested
But it runs about 20-30 min then pc freezes and it takes no command,CPU usage is seen 100% in Task manager
No work can be done until restart,some times even restart is not possible,needs power button press turn off
Well, it’s not for Comodo or its update,it happened without comodo as well,so it’s posted in general discussion here
If task manager is opened it shows most of the cpu is taken by task manager itself ie, by taskmgr.exe and the rest of cpu is distributed among others big programs as explorer.exe,firefox.exe,system.exe etc etc
So it can’t show which program is eating up cpu.
Memory consumption is ok,within its limit although RAM is low i guess 502MB,for Win xp SP3?
Do i need to add more RAM?
As its a laptop it gets hot if run for some time or kept idle
So is it for overheating or for what???
Please suggest any remedies?

Have you ever reinstalled Windows?
If you have same problem after the reinstalling Windows, I think CPU cooler is dead.

Visit repair shop please.