Lion doesn't boot after using Windows 7

I have Lion and Windows 7 installed on my MBP 15 2011. I use W7 only for gaming. Recently I've been having problem getting back to Lion after using windows. Everytime after I reboot or shutdown from Windows, my mac cannot boot properly into Lion (the wheel just keeps spinning at the apple logo screen). Several times, I can get in Lion but then my Wifi doesn't work at all and when I restart, it gets back to the problem above. My only way to fix is to boot into safe mode and use the disk utility to repair disk. I'm not sure if this is a problem with the Resume feature or something else but it's been very frustrating and scaring me of using Windows again. Has anyone got this problem before or can suggest me some way out. Thanks