Not likely a monitor or display issue.
On Seattle (and likely Vegas) boards, this usually means the hard drive is dead. There is a DIP switch to turn on ROM based power up tests. It is generally off as they take a while. When these test are disabled, the first thing that puts video out is the program loaded from the drive, so the board will appear dead if the hard drive isn't working. Eventually, the watchdog bites and resets the board resulting in the reset loop you've noted.
Turn these tests on, and see what happens. If it complains that the disk is bad or gets all the way to the end then resets, the hard drive is dead and needs to be replaced. It's a common failure. Try reseating the cables just to be sure they haven't worked loose, too.