adsl-2 modem and dongle conflict?

hallo,
please bear with me am not big techie

friends pc and my laptop both win 7

friend in next village has pc with adsl-2 modem landline connection to internet that is set to connect immediately the pc is switched on. system very very slow. thought i would try my internet dongle (zte from t-mobile) from my laptop on his pc to see if connection is faster. every time i inserted dongle into pc'c usb it asked for zte installation disc. dont have one, dongle installed automatically on my laptop. also, the pc froze solid.

what i did to try eliminate problem.

i switched off the adsl modem so it could not connect to the 'net when pc switched on as i thought the modem and dongle conflicted and pc got its knickers in a twist. pc still asked for installation cd and froze.

i can take my laptop and dongle to see if reception at my friends village is as good as it is in mine but friend skint, wants to keep pc so we need the dongle to work on the pc before we can decide.

thanks for help - please in words of one syllable for a dummie.

karaman