Reinstalling Vista Home Premium

Computer: 3 month old Dell XPS 420 Desk Top with Vista Home Premium 32bit
I've been having problems with this computer for about 2 months. It often is unstable and rarely wakes from sleep / hybernation. I can't get into Power Options, it always gives me a "Your power options are not available" msg. After numerous attempts to find out what the problem is, including installing SP1, I've decided to follow Dell's advice to reinstall Vista completely. They believe there are corrupt or missing drivers and or files.

So my plan is to use windows back up and save all my files to an external HD, and then reinstall Vista. My question is whether to run the back up recovery right after that and then install all of my software, or do I run the back up recover last.