I'm trying to repair a computer for a friend, and have hit a snag. The computer is running WinXP Media Center, and I think it has a virus. When booted, it gets to the screen with the Windows logo and the "scrolling bar", and goes no further. The bar just keeps scrolling continuously. In order to run a virus scan, I tried a trick I've used before: move the affected drive to the slave position, put another drive in the master position, and do a clean install of WinXP on the "new" master drive, then boot from the master and run a virus scan on the slave drive. I've never had any problem with this method, and have recovered quite a few drives this way. This time, after installing to the new drive and booting without the old drive attached, just to make sure everything is OK with the new install, I shut down and reconnect the old drive. The new install on the primary will no longer boot. I either get a screen telling me that a file is missing or corrupt or it gets past the "scrolling bar" screen and just goes to a blank screen. Unhook the slave drive, and the master will boot normally again. Ideas?