Italian answer follows to ease understanding. :) Dovresti ritrovare i gommini e reincollarli accuratamente, se li hai persi va sostituita l'intera membrana della tastiera. Comunque un consiglio per il futuro: ripulire le tastiere Apple e gli chassis in alluminio è molto più semplice di quello che sembra, basta un panno tipo "ballerina" inumidito, a computer spento un'energica sfregata su tutta la superficie e viene via tutto il sudiciume.
Here's the guide with the related hard drives on sale: Remplacement du SSD dans l'iMac Intel 21,5" EMC 2389 EMC 2428 And here's specifically the 1TB version. 1 TB 7200 RPM 3.5" Hard Drive Due to the relatively small price premium, I'd recommend opting for the 2TB or even the 3TB drives if you can afford them. You're welcome. :)
It looks like the screen might have some problems. If it was not misused, you are under warranty, so get a proof of purchase and club it on the staff members' heads to get the phone fixed for no charge.
Sorry to let you know it this way, but 2010 i3 iMacs are only compatible with dual core i5s: the fastest CPU you can install is the 680. That's because your iMac's socket has slightly different electrical connections (FCLGA1156) compared to the one used on the quad core iMacs (LGA1156). Check ark.intel.com for more informations about the CPUs. I don't know if this could have caused a shortcircuit to the logic board, but PSUs usually "snap" when have a failure, so if you didn't hear anything, maybe the problem lies somewhere else.
As you already tried swapping out the RAM, it could be anything from a bad motherboard to a faulty CPU/GPU. I'd check temperatures with iStat just to be sure it's not something related to a bad thermal paste application or faulty heatsink (heatpipes can leak and become useless if they have blemishes or have been bent), other than that, it might just be a dud. :-D A dead PRAM battery will not cause any freeze during use, so I'd call that out.
What noise does the drive make while the Mac is stuck there? Might as well be a defective or dirty DVD, or faulty drive. Is it correctly recognized by the OS once booted? Do you have any problem booting/reading/burning other DVDs?
Looks like a touchscreen problem, like it's offset or reversed. Happened to me once on my 2G, but I got a cheap, non-genuine replacement that just didn't work properly and had to buy a genuine one. It might also be a compatibility issue, if you accidentally got a 3GS part.