You just did plain old safe mode, right? Not safe mode w/ networking or whatever?
If it came without a disc, it probably has a recovery partition on the hard drive. There's a probably a key you have to press on startup (before Windows starts loading) to get to it (use the googles to find it), but basically, it'll copy the stock hard drive image from the recovery partition to the main partition. This will more than likely nuke anything you have on there, though, so I'd do that later.
If you have a big enough flash drive handy, download ultimate boot CD (UBCD) and install it to the flash drive using unetbootin (makes a bootable flash drive out of a disc iso image), or just burn it to a CD. Boot that up, and use the hard disk diagnostic tool that matches your hard drive brand, see if the drive is going bad. Next step would be to get your data off the drive if you have to, and Knoppix is probably the way to go for that.