Accidently pressed f12 and now my computer goes to the boot screen no matter what, every time I turn it on please help!

I'm running vista on an Acer Aspire M5620 with a Nvidia GeForce 8800 GTS and initially I took everything out for a good cleaning and dusting because one day I went to start up to do an essay and it wouldn't make it past the white screen with the big teal Acer logo. Anyways I put everything back together and it did the same thing but now I accidently pressed F12 and now every time I turn it on it goes to the Acer screen and then straight to the boot screen. I'm going crazy trying to figure this out so any help would be glorious.