Dual boot Windows 7 problem.

I have a dual booting computer with Windows 7 on both the boot drive and the Logical drive [H]. Up until today it worked fine.
I use C drive for normal family stuff and H drive for games etc.
When I booted up today, C drive is available and loads OK but H drive - although I can see it in "My Computer" and Windows disk management says it is "Healthy" - it will not load. It tries to load, I get the Windows 7 logo then a black screen!
How can I get it to boot again so I don't loose all my games and files?
I am a silver surfer and would appreciate any replies in everyday normal English so I can understand what to do!
Many thanks.