Knocked? Can you describe?
Provided everything is secure, minor bumps etc should be (mostly) ok..... but not exactly ideal. I wouldn't expect a GPU or RAM to be going anywhere from bumping into a tower or anything.
Obviously, ideally you'd move it somewhere where it won't get "knocked" but, since you're asking the question, I assume it's not possible?
Any impact to your harddrives though, especially repeated/frequent "knocks" could damage them beyond repair.