Replying to Vegas being superrr slow

so, i just got vegas pro 11.

i am running it on a newer desktop with 4gb RAM, and intel pentium (not the best, i know)

when i first got it, i threw a couple clips into an 'untitled' project (just to mess around), and screwed around with effects, it worked perfect, absolutely no lag.

but then i made a 'project' and put in some clips and started doing just a couple cuts, and it previews slow as shit, like i have tried everything, i have the preview set as low as possible, and im using 720p 30fps footy.

even scrolling through a clip, the audio goes normal, but the video is only half way done by the time audio finishes.

please help!! +K