Very Computer

I've trouble switching between XFree86 and the virtual consoles with my
SPEA Mirage P64 VL (Vision 864). If I start linux with vga=3 in the lilo.conf
(which means 132x43) it works, but after starting X11 and switching back to
a console or just killing X11 I get a blank screen and my monitor tells me
that the signal is out of range. The only thing which helps is rebooting :-(
BTW, vga=normal works without any problems.
Who knows how to solve this problem?

Thanks and bye,
Bernd