iMac has blue line on screen at startup iMac won't turn on any farther than this.  Blue line down the middle and that's it.  Help!
Looks like the GPU is hosed to me. Try restarting it while holding down commandoptionpr and see if that helps. If not, try holding down commandoptionshiftpower button for 10 seconds to reset the SMC. If that also doesn't work, send it to Apple for repair.