startup problem: Grey apple and loading sign. that`s it

Hey.

I tried to install a game on Windows XP on my MBP from 2007,which is installed via bootcamp. The installation failed, so I decided to restart via bootcamp to mac os x(10.5.6). After the chime, the grey screen with the apple appears and beneath the apple is this loading ´sign, whic spins. for about 30 secs, zou can hear that the hdd is loading, but then nothing further happens(but the loading sign keeps on spinning).I once waited for about 4 hours, but still nothing happend.
When I turn off the Mac, it automaticallz starts up (or at least tries to) on mac, without asking me, if I want to run Windows or mac, which rEFIt always did before.
I don´t think that this is a hardware problem, because when I press the option key after the chime,so I can choose between mac and windows, I can start and run windows without any problems. I´m writing this right now on my mbp on windows...
on my mac partition should be everything important like kernel, automator etc.

I would be really happy, if somebody could help me...

All the best.

A flashing question mark appears when you start your Mac

scroll down to the Steps for Mac OS X

bobtomay said:

A flashing question mark appears when you start your Mac

scroll down to the Steps for Mac OS X

Click to expand...

ok, well, but there appears no flashing question mark. should I try anyway?
is there maybe another solution?

when I hit command-v during startup, this ends with:"[...]("/usr/sbin/mDSNResponder",...): no such file or directory.

but when I look it up on the mac partition while in windows I can find thi file.

Does that maybe help?

Yes, these are the troubleshooting steps you should take.

But first, try booting from your OS X disk (put in disc, hold down C while booting), go into Utilities, Disk Utility and run Repair Permissions on your OS X partition.

OK, thanks a lot, I'll try when I'm back home again and let you know what happend!

have a nice day!