My PC Configuration: Processor: Intel Pentium 4 (Prescott) 3.4 GHz HT CPU Cooler: Original Intel 4-Pin CPU cooler which came with processor. Motherboard: Asus P5AD2 Premium Rev 1.02 BIOS Ver 1006 RAM: Transcend 512 MB DDR-II @ 533 MHz HDD: Segate 120 GB SATA @ 7200 RPM DVD-ROM: Samsung DVD-ROM CD-Writer: Samsung CD-Writer GPU: XFX Geforce PCX 5750 with 256 MB DDR VRAM Monitor: Viewsonic 19" CRT Internal Modem: DAX 56 kbps Keyboard & Mouse: Microsoft Cordless Comfort Deskset Cabinet & PSU: Antec AMG 1080+ with 420 Watts PSU. Problem: The above is the system configuration I am using and for the past 3 days whenever I switch on my system after a min or so it restarts automatically. Sometimes "System Failure due to CPU over clocking" POST VOICE message appears and sometimes it doesn't. I don't overclock my CPU and also I found out that my CMOS Battery was low and so replaced it. After replacing the CMOS battery the system was working for more than 15 mins and then when I started the Antivirus Scan which lead to CPU usage the system again restarted. At the time of restarting I found out the CPU temperature (using speed fan & Asus Probe) was at 65 degree C and is BELOW the extreme condition. I can't understand why this happens as 65 Degree C is NOT extreme temperature. So I switched off the system and allowed it to cool. Then restarted the system & checked the CPU temperature in BIOS Power section, where the CPU temperature was at 58 degree C and within 2 mins gradually increased to 61 degree C and stayed there for another 2 mins and suddenly restarted again. I also checked the voltage levels in BIOS Power section and found everything was normal 12v was 11.9v ~ 12.1 v, 5v was at 4.89v ~ 5.01v, 3V was at 3.0v ~ 3.15v and core at (sorry forgot the value but remember that it was in normal). Lately I have another problem also, where the Original INTEL CPU cooler which use to go as high as 4200 RPM doesn't go beyond 2700 RPM these days but still the CPU temperature stays below 65 Degree C. NOTE: previously the CPU temperature use to go as high as 71 degree C during high CPU usage and still system was working fine. NOTE: Arctic silver 5 is used as thermal compound and is there for more than 7 months. NOTE: sometimes the system switches off itself and restarts after 3 secs or so. My conclusion: It seems there is a thermal problem with CPU. But the temperature reading according to Speed Fan, Asus Probe & even BIOS Power section is below 65 degree C which is normal. So its seems its not a thermal problem. Please tell if I am wrong. Also I removed the RAM and reinserted again and the system still restarts randomly. Another thing is after replacing the CMOS battery I did an overwrite of the active boot partition with Norton GHOST backup (as the OS was not booting system abruptly restarts or sometimes booting hangs in both normal as well as in Safe mode) and was able to boot into OS after which when tried to do Antivirus scan the system restarted. I am totally confused and donâ€™t no whatâ€™s wrong. Please help me. Another thing, can I use Petrol to clean the old thermal compound (Arctic Silver 5) from both processor & heat sink or else please suggest which liquid to clean the processor & heat sink . So right now I am thinking of re-installing the heat sink & also thinking of updating my BIOS.