Must unplug and replug monitor after sleep or startup

Hi,
The last week my monitor has been hissing and has now started to remain black after startup or coming out of sleep. I have to unplug and replug the VGA cord a few times before the screen comes back on. It tries to come on on startup but all you hear is this loading hiss and a quick flash of screen. After I get it working it works fine and will even come back on if I play with the on off button. I have already replaced the VGA cord with a new one so that's not the issue. I am running Vista 64 Premium Home on a HP pavilion. I've had the monitor for 4 years with no issues. I have not updated , installed or changed anything before this started. Any help will be appreciated.
 
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