You shouldn't just delete Java's directory
Always uninstall programs through their Uninstaller if there is one, simply deleting the directory might screw up things, which is probably the case here
Apparently the launcher is trying to read modpack.jar from the launcher's Vanilla directory. Which isn't supposed to happen
Try turning off whatever firewall/AV you have and reinstall
Most likely the server's fault
That, or you're just behind TERRIBLE network
Also, this isn't a Launcher bug
I believe everything past the Mojang splash screen is counted as a tekkit/technic bug
That means you'll be distributing some of Mojang's files, which is illegal
OP: What AV have you got installed? Some AV or Firewall might be blocking the launcher entirely
That would get rid of your entire installation, allowing you to redownload it all
Looking through the logs revealed that you've got one of these MD5 Mismatch issues I believe, search around on the forums for a solution for that