grub gone

[Ash Wyllie]

I have an Acer 1 net book that has Windows 7 and Ubuntu 10.04 on the
disk. 

A couple of days ago I had to run Windows (for the 1st time). After I
finished installing a Garmin GPS Add on for Firefox and used it to check
on a GPS, I restarted the computer.

I am not getting to the grub menu. The computer cycles between the Acer
Bios and a prompt at the top left of the screen.

I can boot off of an USB thumb drive. All the partitions are intact and
I can partially access the home partition (permission problems).

So how do I fix grub. I have looked at launchpad.net, but none of the
answers I have seen seem to match my problem, and some of the answers
look dangerous to use.

-- 
                                            -ash
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