|"I wanted to remove the cpu cooling assembly to clean it fully but as I could not remove the self locking bolts I decided to leave alone"|
"Now the cpu cooling fan remains at the high pitch for 10 seconds then it slows down to normal rate in 60 seconds"
At what point did the change in fan RPMs occur, before or after you messed with the cooler? If you disturbed the heatsink on the CPU while attempting to remove it, you probably broke the thermal bond. If that's the case, it means it will now HAVE to be removed, thoroughly cleaned, & fresh thermal paste applied.
Are you hearing any beeps at startup? Unplug the power cord & disconnect all external devices except for the keyboard & monitor. Temporarily unplug all internal drives (hard drive, DVD, etc - both cables) & remove all RAM except one stick. Then try booting up & see if you can a display or get into the BIOS.
BTW, are you are using hibernate, standby, or sleep mode? If you are, that could be one of the reasons it "plays up". Those features are meant for laptops & sometimes cause problems with desktop machines. If you get the system up & running again, make sure to disable all those settings & reconfigure the power options.
message edited by riider