Gigabit Network Suddenly Crap for File Transfers

I'm not exactly sure when it happened, but suddenly file transfers through my wired home network have slowed to a crawl. I have a trendnet TEW-639GR router, and that's the only thing between the two PCs I use, but directly connecting the two makes no difference in speed, either. I'm at a lack of things to test, so I figured someone here might know what I could try. Thanks!

what is the speed the network cards are connecting at?

make sure they are not connecting at 100

you can only set the network speed of the network card but you cannot control the transfer speed.

for testing purposes have you tried to disable the Virus checker?

I would try a few things: Shutdown all the PC's, unplug the router from the wall for 45 sec to a minute, plug it back in (wait 45 sec), then fire up one PC at a time. I would also try running a scan from "malwarebytes", as a safe precaution. Check HDD Disk space, make sure you have atleast 20% (min) free space on the drive you are transferring to. Actually I would make sure you have a min of 20% on both machine's....

Sadly, no such luck, but I did notice something strange... was poking around in the LAN adapter settings, and noticed where I could change the speed; the moment I change it away from auto-negotiation to anything else, it immediately believes that I've got nothing plugged into the damn thing. The only way to convince it otherwise is to uninstall the adapter and restart. Not sure if that rings any bells...