Ok so I used to be able to play Fallout 3 on my PC like 2 years ago. My friend let me borrow his Fallout 3 and I installed it on my computer and I could run it in "ultra" graphics without any lag.

Then once I wiped my hard drive and reinstalled my windows I installed the game again and began playing it in "medium" graphics, and it started to lag like crazy, so then I turned the resolution down and all the graphics options down and it was still kind of laggy.

I'm pretty sure I installed all the drivers I needed after I wiped my hard drive. Can anyone tell me the cause of this? Is it because my PC is getting old now? I also tried to install Oblivion again, I used to be able to run it in full high graphics, I installed the game again and got the same results as with Fallout 3. Same as Amnesia: The Dark Descent, I remember playing a year ago with high settings, now it's laggy on medium.

Can anyone help me solve this problem?