I put the old hard drive back in the computer and made a Win98 startup diskette. Then, I took the old hard drive back out and started the computer from the floppy disk. I typed SYS C: and then pushed enter. Also, I typed FDISK /MBR and then pushed enter, as the hard drive manufacturer's website says to do if there is a "NO OS FOUND" error message. That didn't seem to do any good; when I tried to restart the computer without the Win98 startup diskette, again I got the "Operating system not found" error message. After that, I started the computer from the Win98 startup diskette again and typed C:\WINDOWS\win.com and pressed enter. When I did that, I got an error message that said: Invalid VxD dynamic link call from CDUDF + 00000190 to device "048B", service I. Your Windows configuration is invalid. Run the Windows setup program again to correct this problem. To continue running Windows press Y or ENTER. To quit the current program press N. If you continue running Windows, your system may become unstable. Do you want to continue? Press Y for Yes or N for No: Y When I pushed Y, I got an error message that said: VFAT Device Initialization Failed A device or resource required by VFAT is not present or is unavailable. VFAT cannot continue loading. System halted. Do any of you know why that would happen and what could be done about it? Do you mean that causes it to say "Operating system not found"? I thought that was about problems with storing more than 137GB on the hard drive. My hard drive only has about 16GB on it, so I wouldn't think there'd be anything beyond that limit. How do I find out if my BIOS supports 48-bit LBA? My computer is an HP Pavillion 6633C. If it doesn't support 48-bit LBA, do you mean I will have to reformat the hard drive?