Well, it may be common sence, but try this, it may not bet the problem, but yea
open up FRAP's and go into the movie tab and there should be a small white box under your recording keyBind(button) and make sure it has a tick in it
and let me tell you, if you think you might record, DONT Listen to WinAMP or any music(it records that also) and i lost 4 gig's of great clips because of that