Minecraft stops responding and refuses to close

Minecraft randomly stops responding and when I close it windows says searching for solution to problem but whether I cancel of let it run minecraft will not close. Task manager will not close the window and even stopping the process does nothing. I am using a modded jar so that may have influenced things but I thought I would report this as it has happened several times to me. The only way to close it is to shut down the computer. This does not give a crash report.