Vista - System Restore?

My husband did something to the sound card or the program that creates sound
on my computer. The computer thinks it no longer has a sound device. I wanted
to restore to the point before he did this but it was a few months ago. When
i try to do a system restore to that date it wont let me go back that far. I
am not sure how to do this? Is there a way to restore windows to the orignal?
I bought the computer with windows vista on it so i do not have a backup disk
for windows it jsut came with it, but is there a way i can still re-install
it. Will that solve my problem?