Dim screen, OR power loss during windows boot -- But it's NOT the PSU!

[dgrrr]

An IBM Netcaster A21 (model 2245) running WInXP HOme keeps losing power / restarting mid-boot. It usually fails / restarts when the black screen with WinXP logo appears and the green progress bar starts ticking across. If it makes it 4 seconds or so into that screen, it's fine, proceeds to Desktop and no problems until AFTER the next intentional shut-down or restart.

Another symptom is (less frequent) DIM SCREEN image of same XP boot progress screen, as if at half power.

Obviously I swapped in another PSU. No improvement. (300w should be plenty for 1 hd, 1 cdrom, right? Sheesh.)

It has on-board video (no agp slot) but I doubt that relates.

I've cleared the BIOS, but didn't reinstall or upgrade it yet.

I tried reinstalling WinXP, but no change.

One more detail -- it has a factory installed hidden HD, containing Win98, diagnostics and reinstallation progs. I reformatted the main partition and reinstalled WInXP over it, USING that Win98 "rescue OS". I guess its a clean install -- it says "reformat partition". But the weird thing is, (1) it formateed the partition, installed XP, and THEN converted FAT32 to NTFS...??? why not start with NTFS? Can Win98 not handle it or something?) (2) Finally -- the new installation of XP is SLOW. DUnno why.


So -- about the DIM SCREEN / POWER LOSS DURING BOOTUP:

(1) Do you think BIOS would cause this behavior?

(2) How could a motherboard cause it?

(3) It has on-board video, no vid card. I was thinking of trying a PCI card -- but that's irrelevant to unwanted bootup power loss, right?