Major Database Problem

I have used the same WordPress install, database, etcetera, for the past year and a half. Late yesterday, it just up and decided not to notice the user or password anymore. So today when I tried to switch users for it, that worked, but now it’s giving me the infamous “can’t select database” error.

I go to phpMyAdmin, and my database is there, as is all my content. I am totally at my wit’s end. Any idea of how to fix this?

Thanks,
Lelia Katherine Thomas

P.S. – I know it’s not my server, because other WordPress installations on my server are working fine.