One computer on network getting slow internet

have you tried connecting to therouter with a cable and see if that has issues - helps eliminate if a wireless only issue

also (sometimes wireless does not work with wireless )
- try safemode with networking
as the PC starts keep tapping F8 - a menu appears - choose
safemode with networking - see if that works

For windows 8

http://www.7tutorials.com/5-ways-boo...s-8-windows-81
http://windows.microsoft.com/en-gb/w...ding-safe-mode
http://pcsupport.about.com/od/window...-safe-mode.htm