You could try cleaning the fan on the video card. It might be full of dust and is causing it to get too hot. This can cause a FPS drop. You can check your video drivers for updates through Steam now (at least for AMD/ATI - not sure about Nvidia) or at the manufacturers website. Some cards have been known to lose their usually very thin layer of heatsink compound. If the cooler on the chip on your card is "loose" this could be the case. Some can be easily taken apart and new compound applied - some not so easy. Have you changed any other hardware recently? Maybe check your Device Manager for conflicts if so. If you have an onboard video card you might be out of luck. Some of the recent Steam updates have included various graphic enhancements across all of the HL2 platforms. Not sure what your fps was before but if this is a dramatic drop I would definitely look for video card issues or conflicts with either new hardware or software that has been added recently. If it is an extremely recent issue I daresay that a system restore MIGHT repair the issue if a driver package was damaged in any way. If you are still having problems give us your system specs so we at least have an idea what to expect from it when everything is working OK.