XP service pack 2 2x Maxtor 6 6V300F0 sata drives 1x Maxtor 6 V080E0 SCSI XP is installed on one of the sata drives. A week or so ago, I had an error on startup relating to to a dll for the video card software. I re-installed the software, but since, the computer is running painfully slowly. Hard drive access seems to be increased. Screen refresh is slow. Internet access is very slow, mouse movement lags. There is ocasional lag when typing online. It "feels" like something wrong with one of the HD although system mechanic throws up no errors. BUT when I try to run chkdsk on restart it always skips the processing saying something about cannot check volume. If I try and start in safe mode with command prompt (so I can run chkdsk /f) I cannot get safe mode to load. It pauses while initialising and nothing more seems to happen (waited up to an hour) HD is being accessed, but no progress. Not sure if it help but a hard drive inspector reports a S.M.A.R.T problem "Ultra DMA CRC error rate" on my 2nd Mator sata drive ( none operating system drive). Any ideas guys? Im all out of ideas.

This may help regarding Ultra DMA CRC error rate http://www.pcguide.com/ref/hdd/if/i... What may be of concern is below the part that says --- Today, all modern systems that use IDE/ATA drives should be using one of the Ultra DMA modes. There are several specific requirements for running Ultra DMA:

Are you running the SATA drives in a IDE compatibility mode, using AHCI or have the dedicated SATA drivers installed on install?

I think the HD issues may be a red herring :\ OS seems unstable. It booted in safemode today and was working fine no issues. Went back to normal boot, speed issues again. Everything is so loading. Noticed CPU is fairly constantly running at around 50%. That doesnt seem right. Cant see any applications in task manager eating CPU time. Any thoughts?

Perfmon is used to diag this. Taskman would give some clues also. "Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10