Am having issues with my desktop monitor. Normally when I turn the computer on it goes through the loading process and the monitor displays the status. Recently though the monitor remains blank during the start up and remains that way. The monitor power light changes from standby to power on as it always has and the computer can be heard making all the usual loading sounds.This only happens occasionally but when it does obviously I can't use it and have to shut it down by pressing and holding the power button. I have replaced them VGA cable. When this happens I usually leave it shut down for a few hours and try again and to date it has then worked fine. This seems to be happening every few weeks. Any ideas .?