I just upgraded my Grandma's ECS K7SEM rev. 1 from a Duron 1000 with 128 Sdram to a Athlon XP 1700 and another 512 of Ram.
I updated the Bios and the computer ran fine with with the Duron and extra RAM. After swapping CPUs and booting into BIOS CPU is recognized. However the computer freezes during windows 98 boot screen in normal boot and froze in safe mode when I tried to launch IExplorer.
I replaced the 250 watt with a 300 watt power supply I had lying around with the same basic results.
Does this sound like a power supply issue or OS issue.
It's neither power supply or OS. The faster cpu with 640 of ram is the issue. This sounds like timings are off. Virtually all the time, it's not a good idea to mix different size and maker sticks.
Also, W98 does not like more than 512 of ram. Assuming you now have two sticks of memory:
Can you remove the old 128 from bank 0 (and leave it out), and put the new 512 into bank 0? Try that first to see if it will boot. Go up into BIOS, and change the memory stuff to auto, if it isn't already (take notes on what it was). If that doesn't help:
Have you made absolutely sure that the 512 stick is compatible with Grandma's mobo? (I know it worked with the Duron; but double check anyway.) This is where most people slip up. Call the memory makers' tech support, and ask them to verify.
If you're comfortable rumbling around in the BIOS, ask the mem guys for the default timings for their memory. Tell them the problems you're having. They will probably suggest some numbers. Should be a page up in there to fool with the ram. Take notes!!!! If things don't get better; restore to what it was.
You always have the option to come back down to the Duron, which seemed to be okay.