iMac Mid-2011 (A1311) Model won't boot

[brianm109]

I replaced my stock Seagate HDD with another HDD. Now when I turn on my Mac, the computer does its regular startup chime, but there is no video. A few seconds later, the fan goes on full speed and it just does that forever. I have already tried resetting the PRAM and SMB. I can't locate the diagnostic lights though.

iMac Mid-2011 (A1311)
16GB RAM
i7 (Don't remember exact model)
Radeon HD (Don't remember exact model)

 

[chscag]

I replaced my stock Seagate HDD with another HDD. Now when I turn on my Mac, the computer does its regular startup chime, but there is no video. A few seconds later, the fan goes on full speed and it just does that forever. I have already tried resetting the PRAM and SMB. I can't locate the diagnostic lights though.

iMac Mid-2011 (A1311)
16GB RAM
i7 (Don't remember exact model)
Radeon HD (Don't remember exact model)

First, your Mid 2011 iMac used an Apple proprietary Seagate hard drive and cable (thermal sensor). Unless you replaced it with the same drive, the fans will go full blast. There are ways around that - you can Google for the cure(s). The no video is likely an assembly error or you broke a cable or connector when taking it apart. Go to www.ifixit.com and review the take apart instructions.