Perhaps you could be more specific???
I've played M&B Warband(and more) for quite a few years now, across a bunch of computers and windows operating systems. I've never had that problem. So......what mount and blade game(plus any mods for it) are you actually playing? Perhaps you could try turning down the graphical settings, that is commonly the first thing to try for improving performance. What kind of machine(specs, OS) are you running the game on? Which DirectX are you running the game on? Machine performance shouldn't be an issue unless it's an older computer, but in that case turning off background programs might help.
Someone might be able to help you, but nobody can read your mind I'm afraid.