Flashing Screen

I have a Dell Studio XPS 1645. A few months ago, I started up my computer and when it got to the "Please Wait" screen in the Windows 7 start up, it begins flashing erratically. I am able to start up in Safe Mode fine, but was unable to fix the issue, so I just did a system restore. It happened again last week, and now I am unable to do a system restore as there is no restore point. I rang Dell and they were unable to help, so they sent out a technician to replace the mother board. As I thought, this did not help, it still flashes when it starts up. The advice the technician gave me is to reinstall windws. I want to avoid this, but I seem to have tried everything.

The only thing I think that might have caused this is a USB drive I used before both occurrences.

Any help would be appreciated.