Windows fails to open applications

Hi,

Once I have several applications open Windows XP Professional Service Pack 2 refuses to open further application. I have heavy-weight applications like Delphi and Eclipse open, but the OS has coped with this in the past.

No error messages are reported by the application I am attempting to open, and there are no messages in the event viewer. What is really strange is that once the OS gets itself into this state, it appears that the OS can't allocate enough memory to perform simple API calls. If I go into an application that is already open and try to open the file menu, or right click on the taskbar to open the context menu, nothing happens.

If I close a few applications, then the problem goes away. The Task Manager performance tab indicates that I still have ~1Gb of physical memory available.

I think this could be caused by:

- A memory module is damaged. My memory is comprised of 1x1Gb modules. When the system attempts to allocate memory in the second module, it is unable to. I think this is a bit of a long-shot because I wouldn't expect my PC to boot if a memory module was playing-up

- I've installed something that has put something malicious on my PC. The only things I've installed recently are PRGrep and WinGrep, but unfortunately I didn't make a system restore point, and windows hasn't retained those old restore points. However a full Sophos scan doesn't show-up anything.

Any suggestions on how to diagnose/fix this welcome because I'm baffled as to what is going on.

Thanks,

Frank.