It is always good to troubleshoot. Does the computer you are having the issue with have a wired Ethernet card?
You could get an Ethenet cable and connect it directly to the server or main computer. You can use any Cat5e or Cat6 patch cable. It no longer needs to be a crossover cable. Then check your speeds.
It could very well be a problem with AC, but this is the only surefire way to prove it is not a wireless issue.
If you do not have a long enough cable, you can move either computer closer. Or purchase a long enough one on monoprice.com for abut $2.00.
