Here is what I got. Looks like I need a new HARD Drive. I'm going to have to see if any of the ones I have laying around are compatible.

See full scan results.

 Diagnostics Completed
Hardware
CPU
DVD-RW Drive
Hard Drive
Hardware TypeDiagnostic NameResult
WDC WD3200AAKX-00ERMA0 ATA DeviceTargeted Read Test Failed
WDC WD3200AAKX-00ERMA0 ATA DeviceSMART Short Self Test Failed
WDC WD3200AAKX-00ERMA0 ATA DeviceSMART Status Test Passed
WDC WD3200AAKX-00ERMA0 ATA DeviceSMART Thresholds Test Passed
WDC WD3200AAKX-00ERMA0 ATA DeviceFunnel Seek Test Passed
WDC WD3200AAKX-00ERMA0 ATA DeviceLinear Read Test Passed
WDC WD3200AAKX-00ERMA0 ATA DeviceLinear Read Test Passed
WDC WD3200AAKX-00ERMA0 ATA DeviceRandom Seek Test Passed
Memory I took a HD out of an old Dell  GX280 that I had laying around. And of course I'm having problems with it. Keeps trying to restore system and keeps repeating. I'm running diagnostics on it now. It passed the 1st half with no errors.  After hooking up the HD in the Dell optiplex 755 is their something else I'm supposed to do before booting up?If it has Windows installed you can't simply move it from 1 PC to ANOTHER and expect it to work...
I'd get a new HDD and do a clean install after backing up your data...Ah ha I see. Ok so I have to get a new HD. Got ya. I thought you could just transfer one hard drive to another computer and it just works. I'm such a noob. Thanks for all your help. I'll put this hard drive from the Dell GX280 back in the GX280.I don't know if this means anything. I ran the Data Lifeguard Diagnostics program on the Hard drive. I ran both the quick test and extended test and they both passed.  Making me very confused ;-(Was this on the GX280 HDD you wanted to place in the system? If so that is expected.Yes I couldn't get the Dell Optiplex 755 "the one with the bad HD" to accept the HD from the Dell Optiplex Gx280. i didn't know you couldn't just swap Hard Drives. Now I know you can't. "I'm a computer noob" lol   

So at this point should I give up on the bad HD?   

or should I buy a new copy of Windows 7 and install it onto this drive and see what happens?

People keep telling me try a fresh install? what does that mean exactly?

i'm new at this. I'll do what you guys SAY is best at this point. I have nothing valuable on this bad HD anymore. I took everything off already.I don't have the Windows disk that came with this computer with Windows 7 Home premium on it ;-(If the PC still has the sticker with ID all you need to do is find a disc that matches whats installed...don't buy it just yet...
For some reason the sticker on it is for Windows Vista. I bought it off someone a few years back. I guess he upgraded it from Windows Vista Home to Windows Home premium.  Is it even possible to get a hold of a Windows Vista Home edition these days? *censored* i'd put Windows XP on this computer just to get it running again.

Your thoughts PLEASE  Try a University booksore or Library...

Or call Dell for the restore Media...