Hl2.exe crashing when I try to start Gmod

I haven’t played gmod in about a month or so, but a few days ago a friend and I were going to play, and get an error message saying hl2.exe has stopped working and must shut down, etc., I clicked more info and I saw it had to do with shaderapidx9.dll. Ive googled the problem, and tried everything I’ve come across but nothing is working. Any suggestions? Im positive it isnt my system specs because I ran it before perfectly without problems.

Post your specs.

MS Windows XP Home SP3
Intel Pentium 4 CPU 3.20 GHz, 1.0GB RAM
ATI Radeon X300/X550/X1050 Series

Not the best, but Gmod worked fine on decent graphics before, and nothings changed since the last time it worked. Could it be the new update?

Im pretty sure it isnt specs though