Windows XP Pro problems after reinstall

Hi again, not my computer problem this time, its a friends friend (if you know what I mean)

Anyway, the problem is like this.

(1)Some period in time, the message kept on appearing saying its running out of disk space on drive c. No data are saved on this drive, so cannot understand why its displaying the message. It got to a point where he has only 40MB left, so he reinstalled XP Pro and increased the partition size.
(2)Since the reinstall, every time he closes an application, the screen turns black and switches off.
(3)Now recently,instead of switching off, it turns black, goes into the blue screen displaying: DRIVER_IRQL_NOT_LESS_OR_EQUAL

TIA