My Macbook Pro started freezing all the time & going to sleep on its own for no reason

I've been having trouble for a few weeks with my computer freezing way too often for seemingly no reason - I'm using it exactly the same way I always have with no problems, and even actively trying to have less applications open (which seems to have no effect). I can't always load simple webpages without it freezing and giving me the color wheel and it's just MUCH slower in general. It is seriously making it difficult to use my computer for work or for fun...

It has also started going to sleep on its own - the screen will just go black (or sometimes BLUE) and the keyboard lights turn off, and the only way to get it to wake back up is to close the computer, wait, open it again and click or press a key. It doesn't respond to any keys/clicks until it has been closed and reopened.

It seems to overheat really easily lately as well - but it does not always overheat when it freezes.

SMC reset did not seem to have an effect. Activity Monitor doesn't show anything crazy, everything is pretty much 0% except Firefox around 7-12% as I'm typing this. 246 GB available on my hard drive so that doesn't seem to be the problem either. Right after restarting my computer it seems better but the problems quickly resurface...

I googled for help before posting this and someone had suggested running the command

syslog -k Sender kernel -k Message CReq 'Channel t|GPU D|I/O|find tok|n Cause: -' | tail | open -ef

in Terminal, which they said "Normally the command will produce no output, and the window will be empty." But mine gave this:

Tue Apr 15 21:04:24 My-MacBook-Pro kernel[0] <Debug>: disk0s2: I/O error.

Tue Apr 15 21:04:42 My-MacBook-Pro kernel[0] <Debug>: disk0s2: I/O error.

Tue Apr 15 21:35:04 My-MacBook-Pro kernel[0] <Debug>: disk0s2: I/O error.

Tue Apr 15 21:35:20 My-MacBook-Pro kernel[0] <Debug>: disk0s2: I/O error.

Wed Apr 16 10:56:46 My-MacBook-Pro kernel[0] <Debug>: disk0s2: I/O error.

Wed Apr 16 10:57:03 My-MacBook-Pro kernel[0] <Debug>: disk0s2: I/O error.

Wed Apr 16 12:11:17 My-MacBook-Pro kernel[0] <Debug>: disk0s2: I/O error.

Wed Apr 16 12:11:35 My-MacBook-Pro kernel[0] <Debug>: disk0s2: I/O error.

Wed Apr 16 12:11:52 My-MacBook-Pro kernel[0] <Debug>: disk0s2: I/O error.

Wed Apr 16 12:23:01 My-MacBook-Pro kernel[0] <Debug>: disk0s2: I/O error.

I don't know what that means or if that is useful info to help solve my problem? I just want to know what I can do to make my mac go back to normal!

I ran Etrecheck:

Hardware Information:

MacBook Pro (15-inch, Early 2011)

MacBook Pro - model: MacBookPro8,2

1 2 GHz Intel Core i7 CPU: 4 cores

4 GB RAM

Video Information:

AMD Radeon HD 6490M - VRAM: 256 MB

Intel HD Graphics 3000 - VRAM: 384 MB

System Software:

Mac OS X 10.6.8 (10K549) - Uptime: 0 days 0:24:42

Disk Information:

Hitachi HTS725050A9A362 disk0 : (465.76 GB)

(null) (disk0s1) <not mounted>: 200 MB

Macintosh HD (disk0s2) / [Startup]: 465.44 GB (229.26 GB free)

MATSHITADVD-R UJ-898

USB Information:

Apple Inc. FaceTime HD Camera (Built-in)

Apple Inc. BRCM2070 Hub

Apple Inc. Bluetooth USB Host Controller

Apple Inc. Apple Internal Keyboard / Trackpad

Apple Computer, Inc. IR Receiver

FireWire Information:

Thunderbolt Information:

Apple, Inc. MacBook Pro

Kernel Extensions:

com.digidesign.iokit.DigiDal (8.0.3f1)

com.paceap.kext.pacesupport.snowleopard (5.7.2)

Startup Items:

DigidesignLoader: Path: /Library/StartupItems/DigidesignLoader

M-AudioFastTrack: Path: /Library/StartupItems/M-AudioFastTrack

PACESupport: Path: /Library/StartupItems/PACESupport

Problem System Launch Daemons:

[System] org.samba.winbindd.plist 3rd-Party support link

Launch Daemons:

[System] com.adobe.fpsaud.plist 3rd-Party support link

[System] com.google.keystone.daemon.plist 3rd-Party support link

[System] com.microsoft.office.licensing.helper.plist 3rd-Party support link

[System] org.eyebeam.SelfControl.plist 3rd-Party support link

[System] PACESupport.plist 3rd-Party support link

Launch Agents:

[System] com.google.keystone.agent.plist 3rd-Party support link

[System] com.hp.help.tocgenerator.plist 3rd-Party support link

[System] com.m-audio.mobilepremkii.helper.plist 3rd-Party support link

User Launch Agents:

[not loaded] com.apple.CSConfigDotMacCert-[...]@me.com-SharedServices.Agent.plist

[not loaded] com.facebook.videochat.[redacted].plist 3rd-Party support link

[not loaded] com.spotify.webhelper.plist 3rd-Party support link

User Login Items:

Flux

iTunesHelper

RescueTime

Internet Plug-ins:

o1dbrowserplugin: Version: 5.2.4.18058 3rd-Party support link

nplastpass: Version: 2.5.5 3rd-Party support link

Unity Web Player: Version: UnityPlayer version 3.5.2f2 - SDK 10.6 3rd-Party support link

RealPlayer Plugin: Version: Unknown

Silverlight: Version: 5.1.20913.0 - SDK 10.6 3rd-Party support link

FlashPlayer-10.6: Version: 13.0.0.201 - SDK 10.6 3rd-Party support link

QuickTime Plugin: Version: 7.6.6

Flash Player: Version: 13.0.0.201 - SDK 10.6 3rd-Party support link

googletalkbrowserplugin: Version: 5.2.4.18058 3rd-Party support link

SharePointBrowserPlugin: Version: 14.4.1 - SDK 10.6 3rd-Party support link

AdobePDFViewer: Version: 10.1.1 3rd-Party support link

iPhotoPhotocast: Version: 7.0 - SDK 10.7

JavaAppletPlugin: Version: 13.9.8 - SDK 10.6 Outdated! Update

iTunes Plug-ins:

Quartz Composer Visualizer: Version: 1.2

3rd Party Preference Panes:

Flash Player 3rd-Party support link

Growl 3rd-Party support link

M-AudioFastTrack 3rd-Party support link

M-Audio MobilePre 3rd-Party support link

Old Applications:

None

Time Machine:

Time Machine information requires OS X 10.7 "Lion" or later.

Top Processes by CPU:

5% firefox

3% EtreCheck

2% WindowServer

2% hidd

1% mds

Top Processes by Memory:

545 MB firefox

74 MB mds

57 MB WindowServer

41 MB Mail

41 MB Finder

Virtual Memory Information:

1.88 GB Free RAM

818 MB Active RAM

458 MB Inactive RAM

880 MB Wired RAM

190 MB Page-ins

0 B Page-outs