I have a MacBook (Late 2008) that's been using an DVI-based external monitor (Mini-DVI DVI converter) for the past few months. It's been working well up until today, when at startup the monitor remains black after the Apple and spinning gears. According to the monitor, there is indeed a signal coming through, and interestingly if I connect the monitor to the computer, the MacBook screen flashes blue constantly until I remove the monitor cable. Any clues as to why this is happening? Thanks for any input.