Intel graphic card not booting correctly after upgrading, again

Hello.

I think I haven´t understood something, there's something I must be doing wrong...
I was using ubuntu 8.04 for a time, and I decided to upgrade to ubuntu 9.04. And all was great during a couple of weeks. But then that message appeared again... 'There are updates available. Do you want to install them?' Well, this time can't be so horrible. It's not 8.04 any more, bugs must be fixed, so... I clicked Yes, and downloading and installation began. At the end the question 'System must be restarted. Restart now?', or similar... Ok, go ahead, restart now. I didn't do anything. I didn't modified the installation list, I just clicked 'yes, you should know what you're doing...'. System restarting never happened. First logging out, ok. Second, machine reboot, ok. And next, an ugly message telling me 'graphics system can't be restarted, blah blah blah, next reconfiguration, reconfigure automatically now?'. Uuhh, ok, do it now, if you know how... No, it didn't. Now I just can boot in low graphics mode.
It's the third time it happnes, I can't believe it. Previous times were under 8.04 version. But was the same secuence. I never touched any configuration file, at least voluntarily. I just installed the OS, let the days come, and follow instrucctions, and all crashes again.
Can anybody help me, pleeeeease? It's frustrating, I mean, I like ubuntu, when it run correctly.

Well, bye, and thanks a lot in advance...