Power on light showing but there's no display

Hi Mehul, seems like you have a crt issue. Though these screens are awesome, there is no doubt in my mind your crt is the cause of the issue. If I were you, I would check the tube. Points of a failing tube are...

-broken flyback (is you iMac making a loud buzzing sound when on?)

-dead tube (a crt screen has a tip of glass on the back, if broken, the crt is dead!)

-failing power supply (though not a crt issue, your crt could be taking too much power from the power supply)

If you can here your imac's speakers and the light is on, your crt is probably dead. This is not terrible though, since you probably have a iMac g3 slot loader, you should have a VGA port on the back, just plug your monitor in and have fun on your iMac. Hope this helped!