Hi all,
Long time lurker first time poster.
I've gotten a lot of good advice from here that's helped me over the years but I've hit a wall and wanted to ask directly about my situation and see if anyone has any ideas. I've been restoring this Gateway 2000 4DX2-66 that was actually my first computer as a kid. I finally ordered a new clock battery chip and after slotting that in got the thing back up and running. But the PSU was making a terribly loud noise when it was running so I ordered an identical Power Tronic unit by part number.

However once I hooked that up I found nothing powered on at all anymore. Completely dead. I went back and rechecked my connections as well as the manual for the machine and found I was putting P8 and P9 power connectors in the motherboard backwards. Put those right side up and had the PSU powering up again and had the little green power indicator light on the back of the motherboard toward the I/O lighting up again. But all 3 lights on the Keyboard (Num lock, caps lock, scroll lock) all lit up as well indicating there's some hardware problem keeping it from continuing to POST. The keyboard doesn't respond to anything, no Ctl-Alt-Del, the actual reset button on the machine doesn't do anything. I've stripped all cards, disconnected the serial and com cable connectors from the board, disconnected the CD-ROM and HDD disks and taken the RAM down to 1 stick and the floppy drive. Which all worked fine before I made this switch. But now I've got nothing but basic power and that's it.
I tried removing the CMOS chip again and seating it back. Still no luck.

Any ideas on what I might have done when switching in the power supply? maybe I reset the BIOS with the timekeeper chip coming out? I hope I didn't fry something when I put the P8-P9's in the board backwards. I'm thinking I may have to get another unit at the very least to troubleshoot and test known-good parts and at the worst to replace the whole thing. Just a shame since I just had it working a day ago and it's my OG machine. But that's the way it goes with 30+ year old hardware.

Any advice much appreciated. I can post pics if needed

Thanks all! love this community