Some devices are capable or sharing IRQ's. But if there's a conflict, then that will definately cause problems such as the one you're having. When you're in your Device Manager, see if there is an "!", if so, you have a conflict or improper setting.
Options to solve this type of conflict include:
1) Remove the hardware (through windows, not physically) that is marked, then reinstall it [you can do this by rebooting and letting the hardware detection do it, or through control panel's Add New Hardware, or by running the hardware's install disc - all these may work, or only one may work]. This can often fix itself this way.
2) Manually adjust the setting of the device(s) to have different IRQ's used (some hardware will allow this, some will not). This can be done via Device Manager as well.
DIM POST, STUPID
POST = INPUT $X
STUPID = PEEK 420, 255
IF POST >= STUPID, THEN GOTO H3LL