My monitor has started to go black about twice or more every minute. It lasts for a few seconds and then comes back on again. Sometimes the mouse freezes. Sometimes the desktop becomes garbled when I open a new window. Sometimes the screen goes continuously blank and only comes on again when I reboot. I don't think it is the monitor, because my monitor is also a TV and works fine as a TV. I thought it might be the video card, but don't want to replace it in case it is something else. I have run an anti-virus scan and there don't appear to be any viruses. Can anyone advise.