Boots in blank white screen the flickers?

Does it chime? if not, you might have a logic board failure, or your volume is low. reset the PRAM by pressing "Command" + "option" + "P" + "R" at the same time immediately after you press the power button. keep it presed until you hear the chime twice. if you re still holding aftr 30 seconds, stop, you might have a faulty logic board.

If that didn't ix it, hook up a display to the vga connector at the back to see if you get the same thing?

if it works correctly on the external, then your issue is either the display connector to the CRT or the CRT itself. i can get out one of my imac G3's and try and get guide made for you.

if it's giving you the same thing, then it could be the logic board, the RAM, the hard drive or the software. Try booting up pressing the opion key. if the botloader comes up then your logic board and RAM should be ok. Try booting to your operating system disk and try reinstalling the OS. if it fails, replace your harddrive and try again. If you need a guide for that, tell me, and i'll try an make one for you.