Memory

My client's computer is very slow.
I have done the usual:

Viruse, spyware scan
Disk cleanup
Disk Defrag

I replaced the memory in my client's computer as it was reported to be faulty, but that didn't make a difference! It's a touch faster but it's still slow.
Although I ran TuffTest, and no disk errors, I decided to do a disk test with the manufacturer test - it's a Maxtor drive but they have been taken over by Seagate. However, neither the DOS or Windows version reported that there was no disk in the system!
I am doing a Stellar Smart Early Disk Warning System scan, and that found a disk!
I am fast running out of ideas!
What next?!

 

The computer gradually slowed up and slowed up, but the log I did manage to save is attached.
This is what's been done since:

It's now got 768MB RAM, which it had before (upgraded it to 1.5GB, but, after liasing with my client took the new ones out because that didn't solve the problem)
I reformatted the drive, reinstalled, and then straight away (even though a TuffTest disk test said there is nothing wrong with the disk) ran a disk test via Stellar Smart Early Disk Warning system. Once again, it kept displaying a popup, notifying me the temperature was 46C, and then it came up with 'Error: Access Violation at 0x00422586 (tried to write to 0x000000A8_ program terminated. I have emailed Stellar with the system screenshots and problem details and are waiting for them to get back to me.