OS: Windows 7 32 bit
Processor: AMD Athlon™ II X4 645 Processor (4 CPUs), ~3.1GHz
8192MB RAM, but with the 32 bit I can only use 3.5
DX11
ATI Radeon HD 5400 Series

Tell me if there's more I need to include.

It runs really badly ... and I have a ton of performance enhancing mods enabled. It reccomends medium settings, so that's what I use.

And no, I'm not going on low. EVER

So should it be running well? Cos it isn't.

Did a quick search for Passmark benchmark for your card and compared it to my old nVidia 7600GT(which got pretty mediocre fps in FO3 on medium settings).

7600GT>5450

So my bet is on your GPU being too weak for medium settings.

Try using Configator - http://www.newvegasnexus.com/downloads/file.php?id=40442 - to background load every choice, increase the number of threads used and post your load order to see if we can help. There's no particular reason your rig should have problems with medium settings unless you went hi-rez on all the textures. Also let us know what resolution you're running.

Hmm, did that, nothing really happened My resolution is 1024x768. I lowered it just now to 640x480 or something, and it just made the graphics awful. No stutter fix.

And to the other guy(multiquote fail) I am stupid with computers, what should I do then? What GPU would you reccomend? And funnily enough fallout 3 ran brilliant on medium on this pc

At that resolution, you could probably expect some medium settings in this game too with the card.

Need to have a budget in mind if you want to upgrade. And need to know what power supply you are using...brand and model.

Desktop PCs are easy enough to swap graphics cards on, unless the one you have is in a "slim" enclosure, in which situation, a regular replacement case is part of the wise upgrade process. Radeons use the "hundreds" digit for performance indications, and a "650" is decent, although a "670" is better. "770" cards need a power supply upgrade to go with them. There is a budget option, but it is a poor buy compared to the 670s. you can get an "almost good enough" "570" card. But you do not want a "450", "350", or "250".

How would I find the power supply?

It's all the way at the back, with the power cord running into it. But the label with all of the important information is inside, under the left hand access panel ("left" when you are in front of the case).

AC/230V

If the performance enhancers are not part of the game, that could be you're problem, aswell if you are playing it have NOTHING else running as this slows you're performance down stuff like messenger ect. if you are useing steam that could also slow you're computer down