Cant uninstall Programs

I cant seem to see any of my programs listed in the Add or Remove programs screen, Before that i had installed Avast antivirus software, then my usb devices started malfunctioning , giving me an error message like, unknown device.

another thing in my task manager there are some programs running that i have never seen eg; snmp.exe i dont know how to solve this please can you help.
OS is Windows XP Service Pack 2, Version 2002

Thank you