Restart explorer.exe. Task Manager -> explorer.exe -> End the process. Now, it should restart. If the problem persists, try ending most of the other processes, because there's not much a reason for explorer.exe to take up that much memory.
but I have tried but it did not work and also I cant open any programs I am using command line to access most. Can it be a driver problem or smthing like SCSI dvd rom problem(a friend suggested) if yes what do I haveto do?
Try shutting down, remove the power to the DVD-Drive, and then reboot, then see what it does. However, that's probably not the problem, unless it's constantly running, which you'd probably have had noticed.