This only happens to Team Fortress 2 and no other games.
Specs:
Operating System
Windows 7 Home Premium 64-bit SP1
CPU
Intel Core 2 Duo E4600 @ 2.40GHz 30 °C
Conroe 65nm Technology
RAM
4.00GB Dual-Channel DDR2 @ 332MHz (5-5-5-15)
Motherboard
Dell Inc. 0CU409 (Socket 775) 37 °C
Graphics
S27B350 (1920x1080@60Hz)
2047MB NVIDIA GeForce GTX 750 Ti (MSI) 28 °C
Storage
372GB Hitachi HDS724040KLSA80 ATA Device (SATA) 37 °C
Optical Drives
TSSTcorp CDRWDVD TS-H493B ATA Device
Audio
High Definition Audio Device
(Specs don't seem to be the problem as the game ran fine at around 70FPS on my "AMD Radeon HD 6570" that is what I upgraded from, that was less then a week.)
As for the GeForce GTX 750 Ti on both low and high graphics settings the GPU usage doesn't change at all.
The game jumps around 60-30 FPS no matter how high and low the settings are.
http://i.imgur.com/nSaYHW4.png
Already tried:
Reinstalling Team Fortress 2
Reinstalling/Updating GeForce GTX 750 Ti Drivers
Reinstalling/Updating sound drivers
Updating Windows
Scanning for Viruses
Closing unnecessary programs
Restarting the PC