There are no cables for the wireless (PCI) card is slotted in the back of the pc and there is a little antenae but no cables.
The very first trouble shooting steps is to switch everything off in order PC, router then modem.
then turn the items back on in reverse order
Modem, wait for the lights to flash across then flicker
Router, again wait for the lights to flash and then flicker
then pcs / laptops.
Check the lights on the modem and router are flashing as they should. Don't think the modem is faulty as you can still get on the internet downstairs with ethernet cable attached to the router.
Next step is to check if the wireless card in the pc is still being recognised check in the network connections to see if the wireless is there (As previous message) If its not being recognised then reinstall the driver might be necessary. but then the wireless network will need to be set up again and you will need the settings. Thats when things get difficult! So don't touch the settings until last resort.