No sound - weird error PT9 M-powered

[minotaur]

Hey all

A few weeks ago I bought a new laptop to be able to work faster on my project files - I use the very same M-Audio mobile pre interface (and hardware) as before (W7 Ultimate, Corei7, 8Gb ram). I transferred all my projects with all my data files to my new PC, and four projects (all of those were created on the same day, a recording for an upcoming EP) doesn't make a single sound since, or just the left side is played (in one instance).
Now I'm not a complete idiot with PT9, all my other project files work perfectly, so it's not the hardware that failed. I checked the playback engine, disk allocation, hardware, I/O preferences, and literally EVERYTHING is the same as on those which sound. Bitrate/sample rate hasn't been touched. No hidden track is soloed out (nothing happens if I solo a track out).

The tracks are prompted to go out through the physical out, yet there's absolutely nothing that appear on the master fader.
If I put a plugin into the master fader, the signal miracleously goes over the roof (the VST shows no input signal nevertheless). Still, not a single sound.
Master automatisation is off, output is set up okay, everything is set up okay, and still nothing comes out. If I load another project in, it works perfectly.
I recreated the master fader, didn't help. I tried to record in the project, it records, but I can't listen it back. Everything seems to be working perfectly, but the signal stops between the track/aux outputs and the master fader, so I hear nothing. I have NO idea why.

I tried exporting all the tracks, as soon as I imported them into another project, they work. The problem is, there are lots of tempo changes, partial files, notes, settings and mixing done already that I can't export (or can I?), I'd rather use these project files if I can make them produce sound.

Do I miss anything? Is there a setup I don't think of? Is there a way to force a correction on the I/O setup?
The solution is gotta be in the project file, I assume it simply has an error somewhere on the output.

I don't get it. Please help me!