I have a set up: Router at front door connected to first incoming phone connection. Laptop (Win 8), Kindle, iPad, all working wirelessly in front room. Desktop (Win Vista), same laptop as above, printer, all working wirelessly in upstairs room. Desktop with Win XP in downstairs back room refusing to connect wirelessly, but has been working when connected to router with Cat5e cable. Have tried to get goinmg with borrowed Belkin wireless adapter, no luck. Should I try a different wireless adaptor, a wireless ethernet bridge (Best answer from eibgrad) or get a 15metre Cat5e cable and run round inside house to connect?
Nothing will be better than running a ethernet cable. It will always work and give you no problems.
If multiple wireless adapters don't work it is likely you do not have enough signal. Not much you can do to fix this. You could I guess use a combination. Use a wireless bridge and run the ethernet cable from you PC part of the way to the router and put the bridge on the end of the cable. Sometime just putting in the hall outside a room makes it work.
Still if it is a option running the cable will be worth the trouble