It sounds like you have a corrupt winmm.dll system file. I would first try the Windows System File Checker to see if it can find and replace the corrupt file. You most likely will need to have your Windows CD handy in case it asks for it so hopefully you have a copy.
Another option is to replace the winmm.dll file from another computer or find a copy of it online. Just make sure it's from the same version of Windows if you take it from another computer just in case it varies between versions which it may not. Then you can copy the file to the System32 directory and reboot your computer. You may want to backup the old copy or rename it winmm.old just in case you need to revert back to it. Do this before copying the new file to your computer. If it doesn't help after the reboot then try to re-register the phone by clicking on Start and then Run. Then type cmd and press Enter. Finally in the command box type regsvr32 winmm.dll and press Enter.