My MacBook Pro keeps freezing

I have been having issues with my MacBook Pro freezing for about 4 months now, since I upgraded to Mountain Lion, although I'm not sure if that is the cause. I get these horizontal barcode like flashes of black across my screen and then all the graphics freeze, but my music or movie might still be playing, although I cannot access anything. The only way to get out of the freeze is to hold down the power button. I'm not sure what is going on at all, but I've tried switching from Chrome to Safari to Firefox. Didn't work. I've tried switching off my flash player; it still freezes. I'm really stuck, and the constant freezing is really detrimental to work, so if anyone has any ideas, that would be so greatly appreciated! I'm not always sure how Etrecheck works, but after my computer rebooted this is what showed up:

Hardware Information:

MacBook Pro - model: MacBookPro5,5

1 2.26 GHz Intel Core 2 Duo CPU: 2 cores

4 GB RAM

Video Information:

NVIDIA GeForce 9400M - VRAM: 256 MB

System Software:

Mac OS X 10.7.5 (11G63b) - Uptime: 0 days 0:2

Disk Information:

Hitachi HTS545016B9SA02 disk0 : (160.04 GB)

disk0s1 (disk0s1) <not mounted>: 209.7 MB

Macintosh HD (disk0s2) /: 159.18 GB (39.27 GB free)

Recovery HD (disk0s3) <not mounted>: 650 MB

HL-DT-ST DVDRW GS23N

USB Information:

Apple Inc. Built-in iSight

Apple Internal Memory Card Reader

Apple Inc. Apple Internal Keyboard / Trackpad

Apple Computer, Inc. IR Receiver

Apple Inc. BRCM2046 Hub

Apple Inc. Bluetooth USB Host Controller

FireWire Information:

Kernel Extensions:

Problem System Launch Daemons:

[not loaded] ftp-proxy.plist

Problem System Launch Agents:

Launch Daemons:

[loaded] com.adobe.fpsaud.plist

Launch Agents:

User Launch Agents:

[loaded] com.google.keystone.agent.plist

User Login Items:

Stickies

iTunesHelper

Tunnelblick

3rd Party Preference Panes:

Flash Player

Flip4Mac WMV

Internet Plug-ins:

Flash Player.plugin

FlashPlayer-10.6.plugin

Flip4Mac WMV Plugin.plugin

iPhotoPhotocast.plugin

JavaAppletPlugin.plugin

QuickTime Plugin.plugin

User Internet Plug-ins:

Bad Fonts:

None

Top Processes by CPU:

37.4% iTunes

20.0% Pages

8.0% AppleSpell

5.4% WindowServer

1.5% EtreCheck

1.1% SystemUIServer

1.0% gssd

0.9% hidd

0.6% fontd

0.5% coreservicesd

Top Processes by Memory:

104.9 MB iTunes

57.3 MB Pages

33.6 MB Dock

28.7 MB WindowServer

24.6 MB mds

20.5 MB SystemUIServer

16.4 MB coreservicesd

16.4 MB Finder

16.4 MB loginwindow

16.4 MB EtreCheck