Sudden major performance drop

I was once again messing around with my spare PC, this time upgrading it with my old ATi Radeon I had a few years back. After setting everything up, it was running perfectly, even running Devil May Cry 4 fullspeed on high settings.

I switched on my spare today so I could let my brother play with it, but for some reason, games are loading much much slower than usual and Touhou games freeze at the intro, sometimes the music starts to loop. Before switching it on today, I have not touched it since the upgrade.

I have already tried re-installing the said offending games, but it seems like it still is going terribly slow or not working at all.

Is their any reason why this has suddenly happened?

Posted my specs and settings in attachments.

EDIT: It seems to be going fullspeed again now, but all I did was try Devil May Cry 4 again. Any posts that could give me a clue on what caused this would be highly appreciated.

all drivers are updated correct?
also did your 'vista rating' go up after the upgrades? and how far up?

It didn't go up since it rates the PC by the most weak component (apparently the Dual Core LOL).

Yeah, I updated the Catalyst Control Center which WAS out of date, but it didn't do a thing.

vista

games

major performance drop