My iMac 10.6.8 w/ snow leopard keeps FREEZING/CRASHING??

ok lets see if i can type this without my computer freezing.

SO. to begin, i have a iMac 10.6.8 which also has snow leopard. I have recently downloaded many things, that ended up not working so i deleted them. I dont know if thats whats been slowing it down (the downloads still being installed but deleted from trash?) but lately my computer has been very glitchy. I dont have apple care or whatever, so i cant call.

This morning there was a "software update" so i decided, whatever, i'll do it. When i did, i rebooted and now my computer is freezing like a mother.

It is VERY ANNOYING and i dont know how to fix it. It just freezes randomly to. I go on safari for a minute, freeze, then hold power button to reboot.

or i click on another thing, freeze, hold power to reboot.

pretty much everything sets it off. I need to know WHY!? i have had it for a long time and its never been this bad. Another thing that sets it off is runescape. i play it from time to time when im bored, and now it freezes every time. but runescape isnt the only thing that freezes it, it freezes on everything else to. its so frustrating!!!!!!!!

i dont know what to do!?

i have tried these:

-online downloads for mac cleanup

-restart and hold apple+S

-restart and hold apple+option+P+R

-software update

i dont know what else to do. is there something i can download to clean up un-used apps. or unistall items?

i just want to play my games and have my iMac run smoothley. if anyone can help thatd be awsome.

skype me: castrojake

i just want someone who has had this happen, and fixed to help me out.

its an iMac 20 inch Mid 2007

10.6.8 with snow leopard