[Grey screen after Mojang logo?]

i had it up to 7gb? thats the highest it has been set to?

[Grey screen after Mojang logo?]

so ive recently installed the Technic launcher and played hexxit for a few minutes. I liked it and wanted to go back to play however this time it wouldn't let me play? it comes up with the mojang logo as usual but when it should go the the title screen a blank grey box appears? ive left it for a hour to see if it is just really slow loading but that is not the case? please help! Many thanks
 

 

Here is a print screen :

 

http://prntscr.com/2vun01