Without more information there are far two many causes to list.You say the setup is OK up to the router, how has this been checked? I would suggest the following, 1 Back up your systems to avoid andy risk of data loss 2 ensure both systems are fully updated not only from M/soft but the makers sites? 3 Turn off any wirless connections on your route 4 connect each system one at a time by cable to the router. 5 run a speed test and compair what you are getting, compaired with the speed you ISP is providing as per the package you have.
Anything could be causing this, is it all the time or just at set times each day. but untill you find the cause you cannot solve the problem.The main thing is to deal with one system untill its working fine then do the same steps with the other system.
At that stage you can maybe update your post with details of you ISP, supply to you ( landline or Cable )and your ISP also how the systems are connected to the router.