You will need to provide more details or look for more details such as...
What speeds does router support? 10, 100, 1000?
What speeds your PC supports? 10, 100, 1000?
Wifi anywhere?
If you have a 1gb router or the PC has one as well, do you have at least a CAT5e cable or CAT6?
You can also bypass the router, assign static IPs to the PC and NAS, connect them directly see what speeds you get.
You are more likely to get a speed of around 25-60Mb/s with these homeplugs.