Upgrade to 2.6.31.20 on dual-boot laptops doesn't work

[tudor]

Hi.

I'm new to Ubuntu, which I installed on two laptops that also have
Windows (XP on one, 7 on the other). Everything was fine while I was
running 2.6.31.14, but I ran into problems when I (or rather the update
manager) updated to 2.6.31.20. 
1. The dual-boot system with XP starts grub and I can't get it to do
anything beyond that point. (I can't get much out of grub anyway.)
2. The dual-boot system with W7 proceeds to the point where I can choose
which version to load. 2.6.31.14 works fine, but choosing 2.6.31.20
simply forces the system to reboot.

Any suggestions and help would be appreciated. 

Thanks,
-Tudor

-- 
tudor <tudor at timb.com>