Low on virtual Memory

I’m running window 2000. I have started an automatic backup every night. I use to window backup program to run my schedule backup. Since I have start the schedule backup. Every morning I come in. The computer lock me out and show a message “system low on virtual memory”. Window would’nt let me open any program even when I try to shutdown window it pop up a message “you does not have premission to this” Is this something related to my backup.
Please help me with this problem. I have a bad headache with it.

Thank you in advance

Thomas