Terribly slow new iMac!

Hey everyone! This is my first post on this forum but I thought but as a long time lurker I thought this would be the place. I have an iMac from mid 2011, 2.8GHz i7, 12gb RAM, and a 1 TB hard drive and only 200GB on there right now. Recently (in the last day or 2) my computer has started running terribly slow. The only thing I can think of is I downloaded Counter-Strike off of the Steam client (I'm sure I'm not the only one on there either). Since then It's been running very slow but I wouldn't think that that would necessarily be the cause of it would it?

I've been using Logic Pro for a while now too and now I can't even record any live audio to the program because I get an error (this one to be specific Apple Portables: About the Sudden Motion Sensor) I'm really struggling here. I don't necessarily want to uninstall steam quite yet but that's the only thing I can think of doing right now, maybe a disk repair on the hard drive? I've check the diagnostics on start up too and it's come out clean. Any advice people???

try clean install again!! i had the same issue last year so after clean install, problem solved

A clean install of what? Of Steam or of another program?

New iMac with 12GB flies so it would appear to be software related. Think you are on right track with Steam uninstall.

Well I uninstalled Steam and it's helped a bit but it's still very slow, I'm about to try and restore my computer to an earlier time but I'd rather not just because I've done a lot since then. Any other suggestions before I try this?

Open Activity Monitor and see if there are any processes taking up a lot of resources there may be an application running in the background that is using up all your resources. To open activity monitor, go to Applications folder, then Utilities and it should be there.

Hope this helps!

I've already checked the activity monitoring and I didn't have much going on that was taking up a lot of CPU usage or memory usage or anything like that. Just the normal spikes starting up various programs. Used the disk utility and verified the disk and had a corrupt file somewhere within the HD. I just went in and repaired the disk (holding command +R on start up) and it seems to be working better now but still taking 1-2 minutes to boot up where I had been booting up in 20-30 seconds.

How is the RAM usage doing in Activity Monitor? With all that RAM you have it should not make that much difference.