1. System is probably, what, 5+ years old? Most new hard drives today have 1-5 year warranties. Optiplex is a business system--lots of read/writes, 9-5 plus workday, probably 70+ percent full. It's probably failing. Does it sound any different (mechanical failure)?
2. See #1
3. If the hard drive is indeed having a mechanical failure, the problem will not follow to the new hard drive.
You can run all sorts of diagnostics, repair tools, repartition and format it, and you might be able to fix it; however, I WOULD BACK UP ALL IMPORTANT DATA BEFORE DOING ANYTHING.
Scroll down alphabetially to the W's for your error msg:
Dell? OptiPlex? GX200 System User's Guide
My system is a Dell Optiplex GX200, 733mhz 20gig,128mb and running XP-Home Edition. During boot-upi usually get this error message "Dell Disk monitoring system has detected that drive "O" on the EIDE controller is operating outside of normal spec.Back data and replace HD" Now! (1)what is going on? (2)Is this HD failing? (3)If i copy this HD to new HD will the problem follow?
After this warning appears and you press F1 to continue, the system runs fine.