You're going to have to pull apart the power supply to see what you need. Most likely, the switch is held in place
with plastic tabs you will have to compress, and it will pop right out. That isn't a big issue. Radio shack
may still carry one that works. OR you could scab one out of a broken computer power supply.(thrift shop!).
The big issue is that XP is dead. At the beginning of the year I tried reloading a couple of XP machines.
Nothing but headaches. At that time, updates weren't working. I had to spend hours researching why.
Seems MS knew it was broken, but why worry about a soon to be dead OS? Who knows if you could get
it updated or activated. I have a couple of XP beaters here, and all they do is nag me about upgrading.
I use a Antec quiet case with my music PC. Works fairly well. A couple year old laptop in a docking station works well too,
and it's quiet. Whatever you do, avoid windows 8 like the plague. I just can't seem to get it to behave with Foobar.
XP was easy, win 7 ok. But 8 just is such a pita.