Maybe it's DNS cache, go to start -> search for CMD andhit enter -> type in ipconfig/flushdns, this will refresh the DNS cache, it worked for me a couple of times.
Yeah, why would you use UDP anyway? UDP is for stream and has a lot of packet loss in order to connect to a Minecraft server you have to use both TCP and UDP.
Might be video card drivers, mine disappoined me too, i had a small visual gap between blocks and water looked red, no way to fix it but get a new GPU, if you have a spare GPU laying around you can test it out if the problem is solved then it was your GPU that started dying, if not try deleting the GPU's drivers and installing the latest ones.