Norton, we have a problem (I think the computer is infected)

Hi
We are currently having some problems...

We have Norton Internet Security on a Vista Ultimate desktop with 4GB ram.



Our problems started a few days ago at about the same time that shockwave flash failed and started freezing the browser. Shockwave flash is up to date and is now disabled.

We now have a number of problems including;

The computer will not always hibernate (the screen shuts down but the computer continues to run); 

Norton crashes. We have twice been notified that Norton has stopped because it apparently triggered a process called Data Execution Prevention.

We are seeing periods of slow/disrupted internet;

After closing Firefox the browser maintains some open processes for several minutes;

Some functions are very slow to launch e.g. I just tried to start VLC player and although it was immediately listed in the Task Manager processes list it took several minutes to appear on the screen.

The latest problem is MS Malicious Software Removal tool wont complete a scan, it stalls part way through the scan and wont cancel (I have run a Norton Internet Security Scan which reported a clear system).  The MS Malicious Software Removal Tool is getting stuck on something called C:\System Volume Information\mountpointmanagerremotedatabase whatever that is.


I normally run the MS Malicious Software Removal Tool once a month and it usually takes about 4-5 hours to complete a full scan.
I have tried running it twice today, both times I canceled it after about 2-2.5 hours. Each time the scan started as expected and stopped quite early in the file count.
The only way to cancel the scan was to use Task Manager and once canceled the computer was sluggish because of high CPU load (70-90%) and unusually high ram use. We normally see 40-60% ram usage, once the scans stalled and closed with task manager the ram usage rises to above 80%.

I don't know what to do now, any suggestions/ideas are welcome :-)

 

Regards