when i try to reload a checkpoint the screen gets all black and i need to start it all over again from the begining of the scene

I see your post is 10 days old and I will appologize for that as a comminity memeber.

It seems there is litte help these days due to the negativity toward Ubisoft.

That said, I have seen this same problem posted many times, but don't remember a solution.

You didn't list your platform ..another serious issue with these forums not being separated.

You could send a trouble ticket to Ubisoft, but you will likely get a generic response from Jason telling you to unstall, reinstall and do a host of other things. (If you are on PC)
http://www.ubi.com/us/support/default.aspx

There is also a Q and A here that may help.
The site is confusing and hard to navagate to find what you want, but I guess that is just another perk of Ubisoft!!

If you could let us know what platform you are running, maybe someone can come up with a fix!!