What are the system requirements?
These are the minimum:
* Pentium II 233MHz / AMD K6-2 300MHz or equally powerful processor
* 64MB of system memory
* OpenGL supported video card with 16MB of video memory. (Voodoo Banshee, TNT and up)
* 300MB of hard drive space
The game in theory can run on Pentium 100's with a Voodoo2, but don't expect much performance over 20fps and the loading time to be less than a minute.
So check your videocard drivers, antivirus/firewalls if that is conflicting somehow...possibly reinstall openal and make sure r_bloom is set to 0.