Could be a few things (CPU/GPU overheating, page file too small, corrupt files, driver issues, hardware issues, etc)
I second what Hatchetman said, give it a good dusting, if you haven't already.
Does it happen in other games? (YES: issue likely with system. NO: uninstall/reinstall CoD)
Do you notice stutters/lag when not playing games (like browsing the web, playing music, or videos)? (YES: generally hardware issue (HDD/RAM/CPU) but maybe windows/software issue. NO: possibly driver problem, corrupt directx files, GPU problem, overheating)
When playing CoD, do your fans spin up like it's trying to fly away? (YES: possible hardware overheating...double check with temperature monitoring software!* (if needed, clean the PC and/or repaste CPU/GPU). NO: could indicate other hardware/software faults.)
What are your PC's specs?
Last time thermal paste redone? (if ever, lol)... Usually recommended every 1-3yrs for gaming rigs... depending on level of cooling performance you require and quality of paste, of course.
*Normal CPU/GPU temps, at load, are anything up to about 65-75C (up to ~85C for GPUs). Generally, anything above that (for desktop PCs) is "overheating" (assuming no overclock with appropriate cooling). If load is applied and CPU/GPU temp quickly rises to 90-100C, you have a cooling problem.