How do i know if i have a trojan worm?

Ok so im not at the expert stages of computers.but i know basics... just need some advice... lately.. i have been having serious connection problems... I have a usb mobile broadband modem.3g. its usually reasonably good...but lately whenever i put my cam on in a chatroom or msn the other persons sound is breaking ...or music etc.... also tonight when i plugged out the modem from the usb port and plugged it back in to the usb port,a message came on the screen saying dep. generic detection or something. so im wondering has the modem caught a virus or something????ive heard about worms and one person said it sounds a little like a worm...if so ..what do i do? is my computer ruined?