Clearly something went. Are you upto opening your system to see if you can diagnose what needs to be replaced? Do you have the needed tools and a good work area?
Review this IFIXT guide: iMac Intel 20" EMC 2133 & 2210 Inverter Replacement while I'm not sure this is the problem here it will give you an idea how far you will likely need to go.
If you can get the display clear you should be able to see the diagnostic LED's. Here's the IFIXIT technique guide: iMac Intel 24" EMC 2134 and 2211 Diagnostic LED's. It should help you isolate out how bad it is.
If you are thinking on getting a new system you will want to get to the HD so you can remove it. Then using a universal USB adapter you should be able to salvage your files.
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Can you give us the last four digits of your serial number (on the bottom of the foot stand). So we can identify which model you have. With it we can give you much better guidance.
crwdns2934271:0crwdnd2934271:0 Dan crwdne2934271:0
Sure. *****TENX88 modelnumber: A1224
crwdns2934271:0crwdnd2934271:0 Leinhardt crwdne2934271:0
Apple iMac "Core 2 Duo" 2.4 20-Inch (Al) Specs
Identifiers: Mid-2007 - MA877LL - iMac7,1 - A1224 - 2133
crwdns2934271:0crwdnd2934271:0 mayer crwdne2934271:0