Ubuntu 8.10: booting problem

[Cooky Fly]

Hi all,

I upgraded to 8.10 from 8.04 several 2 days ago, but after that I
usually need to reboot several times to get a normally-running
computer. When I started the computer for the first time, the screen
showed the Ubuntu logo and the progress bar, then before the bar
reaching 100% the screen turned black and there was no video signals
because the indicator light of the monitor became yellow from blue...
and any keyboard input was not responsible. Only after I tried the
reboot button then the OS MAY BE start successfully. However, it's not
good practices to the computer, I think...
Actually I have got this problem months ago when I was trying 8.10
beta, and it made me reinstalled 8.04 later...
Any buddies have encountered this problem? Please tell me how to solve
it. Many thanks!

--
Sk8er Boi
Cooky