[mdlug] Ubuntu 12.4 on Lenovo laptop would not boot up after software update

[R KANNAN]

Hello,

I have Ubuntu 12.4 (originally Mythbuntu 11.4 upgraded to 11.11 and
12.4) on an old Lonovo R61 laptopwhich has been running fine (albeit a
little slow) for some time.

Today I did a suggested software upgrade and it does not boot since
the upgrade. It goes through the grub  menu and after I hit <enter>
the screen goes blank. I tried 'Previous Linux versions' to choose
earlier kernels but they all seem to work. I also tried to get to
consoles but <Ctrl-Alt><F1>... <F6> does not bring up any login
prompt.

I ran the memtest and it seems to run fine as well.

Any ideas?

Thanks