Ok, a few things...
Post your system specs in your profile. the more information you can give about your system the better, including motherboard make and model, etc.
2, the Power On Self Test happens in a particular order (I apologise if you know this, but I have no way of telling whether you do or not).
First, you get graphics card info on some machines, this is followed by a new screen.
On this new screen, you get the name of the bios or whatever usually at the top. It then goes on to test your memory.
Below this, your IDE drives are detected one by one in the order Primary Master, Primary Slave, Secondary Master, and Secondary Slave.
A new screen is produced, on which is a table of boxes showing IRQ information and the likes. The POST is then finished and the computer goes on to load the operating system.
Where in this process does the monitor freeze, and when it freezes, is it only the display picture, or does the computer's activity stop with it?
My apologies for the question and answer session, but you've given us all very little to work with, so we will all need a little bit more information to try to help you.