EXACT same problem here: also a Dell 4550 and Win XP; screen boots to black (no BIOS) after I use Knoppix. Diagnostic lights in back are indicating a memory problem ... I think. (Hard to read those things.)

Am able to solve the problem by opening the PC case and then closing it up again. Maybe that causes the BIOS to re-examine the system fresh again, and kicks it out of whatever "bad memory" state it's in. Your guess is as good as mine.

Would love to know a fix for this.


DR