Hello, I have an older Dell Dimension 4600, 486 PC running XP SP3. In an attempt to clean up the hard drive without formatting I went in and manually deleted several files. In the process I believe I deleted some of the Windows files and System files. Now when I try to boot I get the "Error loading operating system" error. I have tried booting from the CD using a new XP disk and get the same error. I have also tried using UB boot disk and Spotmau Power Suite to no avail. All I can seem to get to is a boot device menu or the BIOS. From the boot menu there is an IDE drive diagnostics option but I get the same error when I select it. The only options I see in the BIOS is to set the HD to auto or off, neither of which have any affect on the problem. I know this is an older PC but I would really like to get it back running if possible. Any suggestions? Thanks, David Cochran I should be noted that by repeatedly tapping F4-F8 at boot up I can get to a screen that shows "Phoenix ROM BIOS Plus Version 1.10 A10 which is the latest BIOS version. Is also says Dell System Dimension 4600i Series, then BIOS version A10, then the Error loading operating system error. Thanks for your help.