Computer restart during depackage leads to an error?

I am using Linux Mint on my desktop and I was installing updates when my computer during depackage started to freeze up as it often does, due to lack of RAM. So I restarted my computer, and tried to resume, and got this message:
Quote:

E: dpkg was interrupted, you must manually run 'dpkg --configure -a' to correct the problem. E: _cache->open() failed, please report.

When I use su to run it, it does not accept my password. What should I do?

One of the updates is for the linux kernel.