Q: 2006 iMac RAM problems?

iMacs are very fussy about RAM. Most experienced users on these forums only recommend using Crucial or OWC (www.macsales.com), if you purchased from anywhere else I 'd recommend returned and buying from one of these two extremely reliable vendors.

Refer to your owners manual, I will assume that is long gone. If I am correct then look on Apple Support sit and see if you can locate the PDF.

Exactly which 17" iMac do you have.....? see > https://support.apple.com/en-us/HT201634

The Early 2006 Core Duo 17" models only supported 1x1 2GB, but would work with a 2GB module in one slot.

The Late 2006 Core 2 Duo 17" models really only supported 3GB, but would work if 2x2 4GB was installed.

For the correct memory spec's and how-to-upgrade, see > https://support.apple.com/en-us/ht1423