RAM Usage At 96% 10 Mins After Boot Up?

My friend has an HP Presario notebook which she is having trouble with and asked me to take a look at it.In short, its Win 7 x64 Home Premium with 2GB RAM and an Intel Celeron CPU (i forget which model of CPU).Unit boots fine, and logs on, but what struck me was it was very very slow. brought up task manager and checked the performance tab and the CPU was fluctuating between a relatively low level of 4% - 10% but sometimes did shoot up to 50% - to be honest, with it being a Celeron I kinda figured this could be "normal" as its not exactly a brilliant chip. - other opinions welcomed on that pointHowever, the Memory usage as up at 1.35GB and continued to rise to 1.89GB - the machine only has 2GB of RAM and it literally took about 10 minutes to do anything.

I did the usual, Malwarebytes Anti-Malware scan - found nothing - Removed the rubbish Norton and installed MS Security Essentials - scanned - found nothing.Removed any and all of the HP Cackware and anything else that looked odd. The finally I removed a lot of rubbish from the MSCONFIG.Rebooted the machine and checked Task Manager again - this time, instead of 88 processes running, I only had 63 running - but yet again, RAM usage was up at 1.35GB. The HDD is not full and has plenty of space.So I felt stumpedDid some reading online and set the value to 1 in the registry.After changing the ClearPageFileAtShutdown value, when I booted back into Windows, the RAM usage was down to 837MB and fluctuated upto abour 1.3GB thought I had sussed it. So one more time I ran MS Security essentials for one last scan - it again found no issue but immediateley after doing this, the RAM usage shot right back upto 1.89GB and above and the problem instantly returned.