My Macbook Pro started running really slow

Question

This week my Macbook Pro started running super slow, taking ages to open programs and giving me the color wheel alllll the time. I've never had problems like this before! I'm not running many applications or doing anything unusual but it's just running extra slow. Once or twice it has also totally gone to sleep while I was in the middle of using it, and I had to wake it back up. It has also been getting really hot and the battery life seems worse...! This is all new, I'm using my computer just as I always have but it suddenly has issues.
The only thing it has been doing for a while is sometimes the screen will go blue - this either corrects itself within a few seconds or if I close my Macbook and then reopen it, the screen is back to normal. This is very rare though and I don't know if it's related to the slowness problem.
What can I do to fix this??
Mac OS X 10.6.8
2 GHz Intel Core i7
4 GB 133 MHz DDR3
I just 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: 1 day 3:59:13
Disk Information:
    Hitachi HTS725050A9A362 disk0 : (465.76 GB)
        (null) (disk0s1) <not mounted>: 200 MB
        Macintosh HD (disk0s2) / [Startup]: 465.44 GB (235.1 GB free)
    MATSHITADVD-R   UJ-898 
USB Information:
    Apple Inc. Apple Internal Keyboard / Trackpad
    Apple Inc. BRCM2070 Hub
        Apple Inc. Bluetooth USB Host Controller
    Apple Inc. FaceTime HD Camera (Built-in)
    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
    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: 12.0.0.77 - SDK 10.6 3rd-Party support link
    QuickTime Plugin: Version: 7.6.6
    Flash Player: Version: 12.0.0.77 - SDK 10.6 3rd-Party support link
    googletalkbrowserplugin: Version: 5.2.4.18058 3rd-Party support link
    SharePointBrowserPlugin: Version: 14.3.9 - 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:
         7%    firefox
         3%    WindowServer
         3%    EtreCheck
         2%    hidd
         0%    coreservicesd
Top Processes by Memory:
    397 MB    firefox
    106 MB    mds
    82 MB    WindowServer
    82 MB    Mail
    49 MB    quicklookd
Virtual Memory Information:
    1.04 GB    Free RAM
    1.04 GB    Active RAM
    1.03 GB    Inactive RAM
    907 MB    Wired RAM
    467 MB    Page-ins
    0 B    Page-outs

Answer 1

The startup drive is failing, or there is some other internal hardware fault. The "etrecheck" output is irrelevant.
Back up all data on the drive immediately if you don't already have a current backup. There are ways to back up a computer that isn't fully functional — ask if you need guidance.
Make a "Genius" appointment at an Apple Store, or go to another authorized service provider.
If privacy is a concern, erase the data partition(s) with the option to write zeros* (do this only if you have at least two complete, independent backups, and you know how to restore to an empty drive from any of them.) Don’t erase the recovery partition, if present.
Keeping your confidential data secure during hardware repair
Apple also recommends that you deauthorize a device in the iTunes Store before having it serviced.
*An SSD doesn't need to be zeroed.