MBR Error + HD4x Video Driver flickering issues

[EuphangeL]

ASUS P5Q PRO

Intel Core 2 Duo E8500

 

I installed Retail MacOSX 10.5.6 but suddenly issues appeared.

 

Well, first of all i installed the new HD48x drivers from 10.5.7, the acceleration seems fine but my screen flickers every 10 or 7 seconds. I dont know why..

 

Second, I unmounted the bootable usb flash drive and without a confirmation message I unplugged it from USB. A warning message appeared that was saying about danger blablabla. After that my USB drive is not bootable anymore. Do i have to leave the drive mounted all the time when running OSX?

 

Trying to boot from HDD for logging in to Windows is not possible. The MBR displays an error (if you want to know the error let me know to take a pic). Now im writing through the PartedMagic liveCD and im running Linux

 

Is there any way to fix MBR or make the USB Bootable again from here? (i mean from PartedMagic liveCD)

 

I need your precious help mates! Million thanks