I am facing a strange problem. I did a fresh install of Windows 7 Ultimate on my PC and since then I can't use any USB powered hard-drives. The lights on the hard-drives do come on and the harddrives give this continuous very low beep, but the harddrives do not show up in my computer. If you leave the harddrive plugged in for a while all I get is "you need to format the drives before use".
The strange part is that the Flash/Pendrives are detected and I can use them to copy/play data normally only the harddrives are giving trouble. Also the harddrives I tested with this PC are detected on other Computers and work normally. The steps I have already taken:
1. Rebooted the PC with the Harddrives plugged in.
2. Reinstalled windows just in case I messed up some drivers.
3. Tried the harddrives on other PCs and they worked.
4. I couldn't test with an external powered harddrive as I do not have one, nor do any of my friends, so stuck there with that test.
Did you install the chipset drivers when you re-installed windows? If not, get them from the vendor's support site and install them. If you did, or that did not fix things, you can try a BIOS update if there is one available.