I've recently upgraded to 4.0x it was all working fine and perfectly for about 2-3 minutes and all of a sudden this happens look in the screenshots, my admin area looks all messed up and so does my main forum page, but 2-3 minutes after installing it was working fine. any idea what going on? 

That is the problem of cache

Clear the cache..

how would i do that? 

Acp/System/Support/Something isn't working correctly.

ah thank you so much! spent the past 2 hours trying to figure that one out

you are welcome...