This iMac came with 2GB of RAM, the maximum, and the loss of one stick could certainly cause the symptoms you describe.
10.6.8 is the highest it can go but one 1Gb, it probably would not even start to install.
When you replaced the HD for an SSD, are you absolutely sure that you did not pull any wires when you were digging around inside?
The camera is particularly sensitive to this on the the iMac.
Try opening it up again and reseating the RAM sticks, remove and replace, to see if that solves at least one of the problems.
Check camera connections while you are in there
Let us know how you get on
My trusty iMac (iMac 4,1) has served me long and well, but is struggling; I seek guidance about what's wrong and whether fixing it is within my reach.
Dwindling secure web browsing options for this 32-bit Intel mac led me to replace Snow Leopard with Peppermint Linux early in 2017, with good results. At that point I ventured inside the polycarbonate shell, replacing a suspect original hard drive with an SSD, shortening boot time considerably.
Something went wrong recently under Peppermint. I tried to reinstall from a DVD; it seemed to load fine but upon rebooting it just kept chiming the startup chime and failing to complete a boot, then chiming again. Stuck in that loop I reverted to Snow Leopard, which also loaded and boots normally, at which point symptoms of the problem show up:
1. It won't update to 10.6.8 (it downloads the update but doesn't install it).
2. I ran the memory test on the install DVD. All reported normal save for saying it has only 1GB of memory (the machine has 2GB).
3. Photo Booth loads but opens with an empty black window with a note that there is no connected camera.
4. "About this Mac" shows only 1 GB of SDRAM; clicking "More Info" and selecting Memory shows the BANK 0 1 GB memory stick but says the BANK 1 slot is empty.
At age 12 this iMac isn't even my oldest (my 2003 20 inch G4 runs Leopard and browses securely under TenFourFox), but these symptoms seem, well, more than just a flesh wound. Would a failed memory stick create all these symptoms or is more amiss here?