Lehk

also check that your .Jar is not corrupt, redownload it etc.

make sure you have java pathed correctly in windows by simply typing >java at your windows command prompt, if it gives you a bunch of info from java then you do, change your launch command to >java -Xmx700M -Xmx700M -jar Tekkit.jar nogui once it is working then switch from >java to >javaw so you don't have to see the console window, or don't if that is your preference.