Computer suddenly slow - Urgent! :(

Hello!
I decided to go to the LAN party my friends hosted, and when I had rigged my PC and started up a game called League of Legends I got super bad FPS. I quickly understood that the game wasn't the problem, but when I scan for malware and viruses it ends up with nothing major.
The SSD is not the problem, but the HDD might be getting tired.
The CPU HSF and RAM is most likely not the problem either, and the GPU is unlikely as well.
What I have found out so far is that it might be my CPU, as it runs pretty hot. The fan hasn't been altered during the 5 min car drive over to the LAN, and nothing is visibly wrong my my system.
Every fan and component seems to be running pretty well, but I still get bad FPS in games, not because of my spec..

I have an i5 2500K at stock speed, and a 7950 GPU also running at stock speed.
They have never been a problem.

ATM whilst writing this my CPU is at 45 degrees Celsius, and is jumping between 40-50 degrees.
My computer doesn't feel slow at all in Windows 7, but the games certainly do.

I think it has to be the CPU somehow.

- Hauk

Edit; Nvm, I have no clue. Thought the CPU was too hot, but after reading a bit I guess not! :)

I still need help, as the PC isn't running games any better.
Idk if a piece of hardware is faulty, or if it's just some software or anything similar.
Please help me!

Thanks for the answer :)

When I got back from the LAN and tried to play the game again, the game worked perfectly.
I suspect the PSU bottlenecked the system when I was over at my friends house for some reason. (Maybe because of the outlets I used or something?)

Nothing was wrong with my PC other than that, so I'll mark this thread as solved :)