There are two scenarios.
1) Try doing Ctr+Space without Minecraft. See if any other programs respond. If so, then they are picking up that command and stopping Minecraft from doing the same. To fix this, see which program responds.
2) This might be your keyboard ghosting. Normal HP keyboards do this sometimes. If you are pressing too many buttons at once, the newly-pressed keys won't register. Only hold down Ctrl + W + Space and see if it works. You may want to try another keyboard as well.
3) It may be some problem with that key. Try switching your sprint key to something like R or F and see if it works.