Grub problems after upgrading

So, basically after upgrading to 11.04 and doing a million things my system works but GRUB is being a roulette. I'll try to make this as short as possible:

Initially I had 6 partitions in 2 hard drives:
In the first drive two NTFS partitions (sda1 and sda2, with labels F and C), one with only files and the other one with a non-free operative system installed (that I rarely used, but still worked).

In the second drive I had 4 partitions: The first one (sdb1, labelled Archivos) was a big NTFS partitions with files only that I used all the time with Ubuntu (this is where I saved most of my files).
Then I had 2 ext4 partitions (sdb4 and sdb2). sdb4 had Ubuntu 10.10, which I used every day. sdb2 was from an older Ubuntu installation that wasn't working anymore, and I'm not sure why I kept it.
Finally sbd3 was an extended partition with the swap area.

So, I decided to upgrade Ubuntu the easy way, but since I was scared of things going badly I decided to make a backup of my whole sdb4 partition with Ubuntu inside. For this I shrinked the sda2 NTFS partition and copied the sdb4 partition in the unallocated space using GParted live CD.

After that I rebooted Ubuntu and upgraded it to 11.04.
Something went wrong, because after the upgrade was complete Grub was all broken: the arrow keys didn't do anything and pressing enter gave me an error.
I tried everything but figured the best I could do was to reinstall grub. Since I couldn't boot to any operative system I grabbed and old Linux Mint CD that I had and tried to install grub from there, but I didn't know how to, so I had no choice but to install Mint in the sdb2 partition (the old Ubuntu partition that didn't work and I wasn't using anymore), and hope for it to install GRUB after finishing installing Mint.

So, now Grub works again, and I can boot to Mint (which I plan on deleting once this is fixed) or Ubuntu 11.04 or Ubuntu 10.10.
The problem is, if I try to boot to Ubuntu there's a 50% chance it will boot to 10.10 and a 50% chance it will boot to 11.04. There are a million options to boot from (different kernels?), but even if I always select the same it's completely random.

So basically, how can I fix this? Both 10.10 and 11.04 are working, but I can't choose where to boot...
If I need to post more information about my partitions just tell me.
Sorry for being too long and sorry for my bad English.