Compaq Or Hewlett Packard Computer keeps shutting down on start up after installing SP3?,

Has it an AMD processor?.

The way to stop the intelppm (which seems to be the problem) from running is to follow these instructions,

Click START - Run - write in regedit click OK - click - HKEY_LOCAL_MACHINE -SYSTEM - CurrentControlSet - Services - Intelppm then right click - Start - Modify and change the 1 to 4 which should then read 0x00000004 (4) then Exit

Install SP3 and all should be OK