ubun2

HD just freezes and locks up causing me to reboot.

Some times it restarts straight away , some times it won't for 10-15 mins.

Its not a HD problem.

The HD is recently new.

AMD Phenom. Ubuntu 10.10

I dont know my way around the distro to make a descent diagnosis.

Im loosing created work every time this happens.

I have up-graded my Ubuntu from 9.10 to 10.04 LTS  -  Now the computer starts but there is now picture on the screen.
 

I had windows vista and ubuntu 9.04 on my machine. Ubuntu has installed grub boot menu and it automatically detected windows vista installation and added it to the grub boot menu.
 
Now i installed windows seven and looks like it screwed up the grub boot loader. When i boot all i see in Windows Seven and Windows Vista from the boot menu (this is not grub boot menu). It is the windows boot menu. Now I can't even access or boot to my ubuntu.
 
How to fix this so that i can get my ubuntu back?

When i installed ubuntu on my windows vista machine, i had two menuitems for ubuntu and two menuitems for windows vista in the grub boot menu. I edited the boot menu list file and set vista as my default boot operating system. So, if i don't hit enter, it by defaults boots into windows.