Hello -

The green power light would indicate that it knows it is hooked up to a computer, this is even more true if it turns yellow when you power down your computer. Can you plug this into another computer, or plug another working monitor into your computer? This will eliminate your computer as the problem.

Check you video cable, have you had it off before the monitor quit?

If it is still not working, at best you are looking at a cold solder joint, I have seen many monitors taken out by them and have fixed a few. I would sugest this to you only if you are aware of the high voltages that can be found in crt devices, even when not plugged in.

If you have not worked with highvoltage circuits I would suggest looking for a new or used one.
Used CRT's are give them away cheap now. Check your local want ads and craigslist.