Hi Scaper 7
do try the usual tests, disconnect hardware that could be faulting. such as dvd drives etc, but leave things in that you need for the machine to function.
quick question, does the onboard sound and Lan still work?
check your power supply, try a different one if possible, bad feed to the mainboard could result in malfunctions
do a good backup and reinstal o/s, it could be some corrupt registry entries/drivers etc, its usually quicker to reinstall than to track down the problem.
good luck