I'm experiencing the same problem in Win7 with 1.8, I haven't open the client for a few weeks but now it doesn't open with my "wallet.dat" file as argument, if I don't use my wallet.dat then the client opens normally asking to create a new wallet.
I couldn't figure out any trace of the error, the application simply appears and disappears in the win task manager.

Luckily I had a copy of the previous version and that one opens without any problem my existing wallet.