Visa slow - HDD issue?

Hi folks,

it may be a coincidence, but I noticed this when SP1 was applied. However, I have since re-installed Vista and get similar issues before I apply SP1.

I use Bitdefender AV and when a scan starts it starts at 30 files per sec but soon grinds down to 1 file per sec, so a scan take up to 10 hours for a scan (with only Vista and Bitdefender installed). Applications can take minutes to load, but, once loaded, seem to run fine. I can forget trying to access the internet as it can take 10 minutes for Google to load!

It seems to me that Vista runs fine until I need to access disk-based data, but that may be just my perception. The computer logon and off appear just fine so I am unsure about this.

I have used Driver Detective and updated all drivers it flagged as out-of-date.

As stated above, I have re-installed Vista, and it seems to work fine up to the point where I start to load applications, then goes back to this slow state.

I have bought a new HDD and get the same thing. The disk is an s-ata, and I have swapped cables and put the disk on another controller. I have run chkdsk and defrag on both drives.

4Gb of RAM passes memtest, so I don't believe it is a RAM issue either.

The only thing I can think off that I haven't tried is to flash the BIOS, bit I am a bit wary about this.

Does anyone have any ideas as to what I should try next, or is it time to take the beast to Computer-Repair-Man?

This computer is a is custom build.

Hope you can help

Art