Unfortunately it appears that TP-Link's site is down, I was going to suggest that you make sure you have the latest driver as well, however if you have disabled the wireless and tried a wired connection and still have the shoddy issues then I'm doubtful that would help. Sounds to me like perhaps your tcp/ip networking stack has something bonkers going on.
1. Run elevated command prompt.
2. Type "netsh winsock reset" and press enter.
3. Restart computer.
Other things to try:
1) Run "sfc /scannow" at an elevated command prompt, allow it to finish and repairs needed.
2) "netsh int ip reset reset.log hit" at an elevated command prompt
3) System restore back to a time when you think the connection worked