[dmcd]

I had a similar problem with my old installation of XP Pro not recognizing an external backup drive. I mucked around for ages to no avail. Something had become corrupted. I couldn't allocated a drive letter to the external drive. I finally downloaded a trial of Zentimo which helped solve my problems and I actually then managed to reset all drive fixed letters plus several backup drives and things like the Kobo and memory sticks with unique letters from the second half of the alphabet once I could access that drive on that particular USB port.

I suspect some uninstall or other ripped out something pertinent.

Could you try an XP repair from disk? You will lose all your personal settings preferences, but all your programmes and data should be safe. Always, always do a backup of data, just to be absolutely safe when mucking around like this. In my case, the repair wouldn't work though because of numerous updates I suppose.

After a dead hard drive, I'm now running Win7 Pro (and hating it with a passion) and having no problems with Kobo or any other external device, but I did go and buy Zentimo just to be safe in the future. It's a nifty little bit of kit.

Then again, it might just be easier to transfer your books from the PC on to a stick, plug in to the laptop and load from there.

Good luck.