i5 2011 iMac: Inconsistent, Strange Problem (Screen, Input, Startup, etc.)

[BlackBulletIV]

Over the last few days I've had a really strange problem with my iMac. It's very inconsistent, so my descriptions of it will probably be long. I'm just wanted to know whether anyone has experienced something similar, or an idea of what the problem is.

It started happening a few days ago, only here and there, only on my Windows partition, and only while processing 3D graphics in a game. The first time the screen went all blue and some really crazy flickering that made my eyes sore; I had to do a hard restart, as the Mac wouldn't take any input. Other times it would take input, but part of the right side of the screen was appearing on the left side, and the image was distorted. Still other times it would black out with vertical lines of grey or other colours, not taking input.

This morning it happened on Mac OS X for the first time, just when I finished watching a YouTube video. The background was white and the lines were grey; it wouldn't receive input. Later in the day the screen would keep blacking out, with faint vertical lines, as soon as Windows or OS X started up. Then, if it did actually boot, OS X started taking ages to launch, far longer than Windows.

Now neither OS X, nor the Recovery partition, will boot; they just get stuck at the plain grey screen right before OS X normally shows up. Only sometimes will Windows not black-out before launching.

One final thing I've noticed is that it didn't seem to happen in the morning. I doubt anything thing will change in the morning now, considering how bad the situation has got today.

Anyway, thanks for reading. If you have any idea what the problem might be please let me know. My best guess at the moment is a logic board problem.

My specs:
Mid-2011 iMac 27"
Intel i5 3.1 Ghz
8GB RAM
1TB HDD
AMD Radeon HD 6970M 1GB

 

[leman]

You should probably bring it in for repairs From what you describe, the problems may range from defective PSU over problems with logic board to a bad graphics card.

 

[BlackBulletIV]

Unfortunately, I live way out in Mildura, six or so hours from Melbourne where the nearest Apple Store is. I'm most likely going end up shipping it or something.

 

[BlackBulletIV]

This is really interesting. Now, first thing in the morning, OS X will start up, but extremely slowly. Once that's done, OS X seems to run very slow in general. I can't see anything strange in iStat Menus; CPU, GPU, memory, fan speeds, temperatures, they all look fine.

It just keeps getting weirder.

 

[techno96]

Always give a PRAM reset a try, can't hurt. Hold Command Option P R at boot

 

[BlackBulletIV]

I've done that now, but it didn't help. I also tried a few SMC resets, but I don't think it did anything.

I've taken it to my local Apple service provider (thankfully there is one in my area), and they're taking care of it now. They said they thought it was either the logic board or the graphics card. Hopefully it'll be sorted out soon.