ok msacm32.dll is a module containing functions for audio compression for 32-bit applications.
They can become corrupted or be removed from your system by removal of a piece of hardware or uninstalling another program or can be disabled by the Isass trojan/worm.

The first question is ...Have you ran any antivirus programs to see if there was any presense of a worm/trojan/virus.

Have you tried a system restore to go back to when it was working ok?

another way is by running "system file checker".
start > run and type the following in the box

SFC /scannow

(notice the space) Click OK and let the files be replaced from the built in program. This works on some computers without the use of an installation CD but some will require the XP installation CD (not a restore CD)

Otherway:
download the msacm32.dll in zip form and open the zip program.
choose Extract
in the destination folder type the destination path for the operating system that you use
C:\Windows\System (Windows 95/98/Me)

C:\WINNT\System32 (Windows NT/2000)

C:\Windows\System32 (Windows XP)

Then reboot your computer

If the problem still persists then

start > run > type cmd > enter and then type

regsvr32msacm32.dll

and press Enter and if asked to overwrite any existing files check ok