Ok, multiple issues with my PC.
Configuration : P4, 845 GV motherboard, bios version VA84510A.8GA.0023.
P08

1. It switches on directly on stwitchin on the mains(without having to

press the power button on the CPU)
2. On turning it on, it displays the message : "CMOS/GPNV checksum bad.

CMOS Date/Time not set" (changing the battery didnt help)
3. The monitor(SAMTRON) keeps giving the message "Control lock

locked/unlocked" intermittently.
4. Also get"CPU was previously shutdown due to a overheating issue"

message, once in a few days.
I have 2 Hard disks - 40GB Samsung(Primary) and a 250GB

Seagate(additional)
I installed SpeedFan and it shows me that the the seagate hard disk

gets heated very fast, often reaching 50 deg celcius withing an hour or

2.

You possibly have a number of serious errors:
Failed CMOS battery. About $3.50 (US) at a major store like Wal-Mart, Best Buy, Circuit City. Etc.
Then you either have a failed CPU fan, or failed connections to the fan, and probably thermal past dried out or missing.
Then you need to evaluate whether the hard drive is bad, by downloading the SeaTools software from the www.seagate.com site and test your drive... or switch drives with the 250 GB and reinstall it as Master.

Your CMOS problem May be that your battery holder is no longer connected to the board. I have had this happen, the battery holder gets shorted (opened) and the connection goes bad. Each time you restart the PC it has lost the time and date. This one flaw will not stop your PC from working. You just have to reset the time and date each boot. Also, put in a new CPU heatsink/fan (upgrade to Zalman or a same quality) brand. Don't use the Seagate anymore.