OS (C:) space left changing almost every restart.

Hello people of the forum, I have joined to seek advice on an issue that is currently just annoying, but may develop into something worse.

I am currently have a 456 gigabyte hard-drive. The problem I have is that almost every restart of my laptop the value changes from one value (currently 52.3 GB free as I type) to a completely different one (around 237 GB free). It is always either one value or the other, with both increasing or decreasing the exact same amount depending on what i've installed or uninstalled. I was wondering if there was a way to find out which was the correct value, how to solve the problem or to know if this may cause problems if I do have a large amount of space left but my laptop will not recognise it and refuse to let me install programs.

Any help is appreciated, with the research I have already done on the topic (mostly browsing the little forum posts there are) and the following solutions from the pages below have been tried with no success :

Hard disk space keeps changing randomly - Microsoft Community
Hard Drive space keeps fluctuating - Windows Vista
My harddrive space keeps changing? - Yahoo! Answers

All help is greatly appreciated.

Thanks so much for replying, I was losing faith haha.

To see my hard drive space I am using Start->Computer then looking at my hard disk drives (of which there is one).

The only thing I have plugged into my laptop is the powery-wirey thing that goes in the back to charge it. I have the battery taken out of the laptop because it's plugged in, but the value still changes wether the battery is in or not.

I have taken two snips, one when the computer thinks it has 58.6GB left and (after a restart) another when it thinks it has 214GB left

both again (by accident) with the thing Layback Bear asked for

Just messed about in Primal Carnage for 5 mins, no change in the hard drive space.