The only time I've seen the limited or no connection balloon in Windows is when the physical cable from the PC to the switch/router/hub is running dirty (taking errors) - cable could be bad.
I'm not sure when you see the issue, but a questionable cable seems to act-up when there is heavy load placed on the wire.
If it worked fine for a few days/weeks then started to occur and seems to be random, there's a chance the port on your computer or switch is going bad (new port on switch? try another?).
If this doesn't seem to help, please explain your network setup more in your reply.