Iv'e seen this happen. A couple of things can go wrong, the first thing I'd check is the condition of the pins in that plug, the part where the adaptor connects to the console, although usually the problem with that connection is on the adaptor, not the ps2, so more likely, you've blown onboard fuze PS9. That one is for the adaptor and hard drive 5vdc, those blow (I've done it more than once) without affecting the ps2, otherwise, it'll work, but not the adaptor or hard drive.
Sounds like what's wrong to me.
Don't bother with the usb adaptor, those are for 10k consoles only, as far as I know. If you give up that ps2's version or SCPH_xxx.xx number, I can cough up a fuze diagram that'll show you where PS9 lives on your board, but they're numbered with "PSx" numbers, the one you're looking for will be near the plug I talked about, though, regardless of what model you have, LOOK.
A toxic agent on a dangerous mission so secret, even I don't know what it is, because if I did, I would have to kill myself. I don't even know who's side I am on.