The restore points only go back a little bit over a week (the problem began before then). I tried the registry fix, it wasn't in there so I added it and it still doesn't work.
Also, I noticed that one of the computers I have isn't in the same workgroup (though it still connects fine to the server). The problem computer can see that one, but none of the others. Also, all of the other computers can see the problem computer.
Thanks for your help!