I'm running Win7 Corp x64 with 4gb on a Dell Optiplex 755 (Core 2 Q6600). When I run chkdsk /f on the C: drive (it runs during start-up after a reboot), then the problem goes away for a day or two. It always returns, though. I was convinced that I had a failing hard-drive, so I got a new hard drive and restored an image to it. After a couple of days, the problem started on the new hard drive. The error it gives is 0x8100002F. I am backing it up to a 1.5TB Seagate FreeAgent via USB. Here is the error log: Windows Backup skipped C:\ because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Documents because is it on corrupted drive C:\. Windows Backup skipped C:\Users\Public\Documents because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Music because is it on corrupted drive C:\. Windows Backup skipped C:\Users\Public\Music because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Music\Powerman 5000 because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Music\Thousand Foot Krutch because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Music\Five Finger Death Punch because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Pictures because is it on corrupted drive C:\. Windows Backup skipped C:\Users\Public\Pictures because is it on corrupted drive C:\. Windows Backup skipped C:\RightNow because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Videos because is it on corrupted drive C:\. Windows Backup skipped C:\Users\Public\Videos because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\AppData\Roaming because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\AppData\Local because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\AppData\LocalLow because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Contacts because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Desktop because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Downloads because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Favorites because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Links because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Saved Games because is it on corrupted drive C:\. Windows Backup skipped C:\Users\jhankins\Searches because is it on corrupted drive C:\. Running chkdsk and rebooting is a temporary solution. Chkdsk never finds a problem. Please don't suggest it. Obviously, my drive is not corrupted. That means that this is some other failure combined with an erroneous error message. Is anyone working on a fix for this? Thanks, Jamie

Antivirus program may block the access when the backup program is checking the C drive. I suggest you temporary disable or remove the antivirus and check the result.Arthur Xie - MSFT

I don't think so. I only use Microsoft Security Essentials. Also, once it starts doing this, it does it every time until I run chkdsk again. Once I do, it's fine for a couple of days.

I noticed that Dell does not provided Windows 7 compatible drivers for this model. I suspect that there are hardware problems. You may download SATA driver for your current hard drive from the following website. Drivers & Downloads for OptiPlex 755 Important Note: Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information. I noticed that you have replaced the hard drive. Did Dell help you in it?Arthur Xie - MSFT

As you said, there is no Windows 7 driver. I installed the Vista x64 driver, which doesn't help. No, Dell did not help with installing the hard drive.