Team Fortress 2 Pc requirements - DirectX® 9, Windows® Vista/XP/2000
http://gamesystemrequirements.com/
League of Legends -
Recommended System Requirements
•3 GHz processor
•2 GB of RAM (Windows Vista and 7 users should use 4 GB of RAM or more.)
•12 GB available hard disk space
•GeForce 8800 or equivalent video card (Dedicated GPU with 512MB+ Video Memory(VRAM))
•Support for DirectX v9.0c or better.
•Windows XP with the latest service pack installed, Windows Vista with the latest service pack installed, or Windows 7
•The latest update to .NET Framework from Microsoft
https://support.leagueoflegends.com/entries/234272-system-requirements
Both those games are still, really, Windows XP games prefrably rather than anything else. Team Fortress 2 is not even Windows 7 compatible, assumedly, so if you are using Windows 7 the game would be rather slow and not fast. You might try a lower resolution as it would nmost likely prefer 800 x 600 or 1024 x 768.
League of Legends is a good game but better played on Visrta than Windows 7. It's still a basic Windows XP game. again, compatibility mode would most likely give better results as well as a lower resolution, perhaps 1440 x 900 would suit it better.
Consider updating your .Net framework or even try installing a previous version, 3.5 (leave whatever .Net you have installed, though).
http://msdn.microsoft.com/en-us/vstudio/aa496123
If you want continued "advice" please add all of your PC specs however, any replies given are still only for consideration.