Broadband is slow after removing a network place

[Lomax_UK]

About a week ago, a friend plugged their laptop into our network just for a few hours.  Then we unplugged it and returned the cable back to the computer we took it from.  Ever since this has happened, our broadband connection has been very slow.  Is there something that can be done to speed it back up again? Thank you in advance.

[ian.miller]

other than Mr piper's very helpful answer.

Is the network generally slow? and did you have to change any setting to accomodate the laptop?

It sounds like the other PC's might be still trying to hunt for the laptop on the network even though it has been removed, what is the make up of the network. Or (and this is extreme) the laptop added a virus/trojan to your system that is using up your bandwidth.