What's dragging my computer down?

Hi, I'm new to this forum (and all forum posting). I wasn't sure whether to post here or on gaming.
My computer was built for me by some guy about 6 months ago and its been bugging me for quite some time now that it seems to have low capabilities when I'm gaming. Here are the specs:
Fitted Motherboard:
ASUS P5G41T-M (LX2-Series) Socket 775

Processor:
Intel Pentium Dual core E5800 3.2GHz per core

Memory:
Single module 4 GB DDR3 running @ 1333MHz (maximum capacity 8 GB)

Hard disk drive:
1TB (1000 GB).

Video card
PCI-express ATI Radeon HD 5450

Operating system:
Windows 7 Ultimate 64-bit

Now, on The elder scrolls: Skyrim, I have to run the graphics on default low settings, as well as lowering the res to 1360*768 (from 1920*1080)
If you would like information of the settings I have to run any other games on just ask. Please, tell me what's dragging my computer down.

Please perform the following, so that we can get the exact specs of your computer. This will better assist us in helping you more.

Publish a Snapshot using Speccy

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Here s is: http://speccy.piriform.com/results/O8BkORDKbGOaKsw8gEL8GWc

For starters I see that one your partitions is nearly all used up. If it has windows on it, then that can cause issues.

Does this really slow it down that much? I use that disk for backup should I get hold of an external hard drive? and will this really increase the speed by a lot?
Thanks for the help

So is it one drive partitioned out, or is it 2 separate physical drives?

Skyrim is very GPU intensive.

In addition to cryptodan's suggestion, you could probably stand to upgrade your video card. I have a quad-core oc'd to 3.2ghz w/ 8gb ram and a Radeon HD 5570 (card similar to yours) -- my settings in Skyrim have to be set relatively lower than what I would expect, and I know its not my CPU/Ram.

Cheers guys and yes, its one drive partitioned out.

Well if its used for back up, it is not a good idea to partition the drive and use the same drive as back up. If the drive suffers a catastrophic failure your data is lost. I would recommend that you get an external solution and remove all partitions then reinstall Windows.