BleepingComputer.com: Screen goes to black after starting

Hi Guy's
I have an ex lease 3gh IBM 8172 small desktop 1gb ram ,250gb H/d ,XP pro . about 2 mths ago I started to have intermittent freezing problems & Task Mgr showed no problems & last week Pc started to work very hard & kept rebooting itself & I used the power button to close it down, I thought , as I had a DVD burner problem recently I changed the burner to a CD R/W & now PC starts after a message & I select start Windows normally it boots OK but screen goes black within 30 sec's but power light still on . Tried another H/D & same problem .
One thing with this PC is it always showed two drives in Device Mgr & I disabled the non existing drive as it used to show up in My Computer as Drive E or something like that . Is this a power unit problem ? Or should I be looking at some other H/ware problem ? Can I save the old girl ? Should I try rebooting without Burner connected ?

Cheers Ozi