I think that we need to eliminate the RAM issue. TheDuck has a good idea as well, I use an Ubuntu CD as a test.
Also, set the BIOS to boot Floppy, CD, HDD and turn off all the power saving, snooze and screensavers.
The PSU is on the low side, but the symptoms don't really match that sort of issue..............I would expect you to get a little bit further.
I have used ASRock MoBos with no problems in the past. In fact I have a K7VM2 and a 2400+ Athlon about 3 feet from me right now They are the "economy" version of ASUS and belong to the same company.
It is possible to get a defective MoBo out of the box. I have never had this happen to me, but my mate has had three this year....................confirmed by the supplier.
Noia has a good suggestion. I keep it on a bootable floppy (several!)
I have it in my bookmarks: http://www.memtest86.com/
WARNING: it does take a while to run