Ubuntu 11.10 - OS freezes, hard drive turns off?

Quick timeline: Ran Ubuntu 11.04 using Wubi for a few weeks, loved it as my main OS. I waited until 11.10, then partitioned my hard drive using the Ubuntu 11.10 installer - installed successfully alongside Windows 7.

However, I am experiencing frequent problems with 11.10 - the OS keeps freezing. After logging in it will freeze at some point, and there is nothing I can do - no menu options work, no keyboard buttons respond (Num Lock, Caps Lock work). My mouse is the only thing that moves, except it won't do anything when I click on things. My only option is to hold down my laptops power button, do an emergency shut down - as a result, Ubuntu then refuses to boot. I reinstall Ubuntu and the circle continues.

I think the cause is somehow related to my hard drive - I'm sure I can hear it turn off when the freezes happen, and my hard drive activity light stops flashing.

I'm using an Acer Aspire 5542 laptop on Ubuntu 11.10 64bit.

I've tried everything I can, I would be incredibly grateful for a solution.