IMac freezing

That is odd... I hardly ever come to this forum, but today I did.. wanting to post almost exactly the same question.
My 2.16Ghz iMac 24"with 2Gb SDRAM in it does almost the same. Strange lines appear, sometimes only in a window, and sometimes across the screen.
The weirdest thing is that I can take screenshots of these lines:
http://www.hofhuis.org/meuk/scherm.png

My Mac tends to crash when I minimize windows during the genie effect (yellow ball).. it crashes halfway the effect. It also freezes when I do processor tough calculations, like converting movie files etc.

It feels to me that it happens when me Mac gets more used and warmer. After I start it up, all is fine. But after a while the lines start to appear, then a while later windows start acting up, and then it just freezes.
And it is getting worse and worse with time... I tried installing a new OS, but no dice... it even gave the lines while starting up from the installation DVD.

Ehm, this actually turned into a whole seperate post.. sorry 'bout that.

It is common problem, you can find more searching forum with "horizontal lines" keywords.
Your Mac has failed GPU and need main board replacement - cost ~800 USD.
Apple refused to start a replacement program despite of large number of failures.

This thread might help though... will try it out later tonight:
http://discussions.apple.com/thread.jspa?messageID=7128445&#7128445

And it looks like a downgrade to Tiger might be a bonus.

Those threads should explain little bit more:
http://discussions.apple.com/message.jspa?messageID=7204009
http://discussions.apple.com/message.jspa?messageID=6934553
http://discussions.apple.com/thread.jspa?threadID=1096520&tstart=0
and finally:
http://discussions.apple.com/thread.jspa?messageID=7301179&tstart=0
What is interesting, my iMac wasn't used excessively and it seams to be rather material/production problem.

Hi Paratrooper... I did this:
Installed SMCFanControl and I have my fans running fast (31C temp 3515RPM).
In the meantime I am running BOINC Seti.. eating up 100% of my cycles.. and sofar no problems...

people, totally off topic but i cant figure out where the POST A QUESTION is.... and if you can answer it here then cool. I upgraded my ram on my imac. The thing is, i want to sell my old ram. would i need it if there was a malfunction on my mac when i needed to ship it to apple?

Hi Manuel,

I have no clue how to post a new topic here. RAM is something that you are allowed to change in your Mac... it is not like a logic board. So you do not break your warrenty is you replace it... so the answer is.. you can sell it.

TheDesmodus wrote:
I have no clue how to post a new topic here.

*Hi Desmodus, Welcome (Back)* to Apple's Users Help Users Forums. 🙂

You are currently on a Topic = Thread Page.
Go back 1 level to a Forum page and find the button on the upper left. If you err and go back 2 levels you will be in a list of forums or the Category page w no capability of posting at that level. It takes a while to get used to how all this is organized. Hang in there. 🙂

Good Luck, JP 🙂