Iphone 4 white and blue lines

hi,

ive got an iphone 4 and today the phone wouldnt turn off for ten minutes, it was just stuck on the application i was running - then it went black and now the screen is black with some white horizontal and vertical lines and also has thin blue lines. the phone is completley unresponsive to charge or pressing any of the buttons. it is also quite warm. the phone is in good condition, has never been dropped or banged and has no damage that i know of.

hope you can help

thanks

conor