Can you explain what is happening? Are you getting any error messages? If it is not a username/password issue, generally this happens when you have a conflict of some sort.
Give the steps in this tutorial a try to eliminate any possible theme or plugins conflicts:
LOL -- yeah, can't take credit for that -- that's just what it has been called. It does catch the emotion one feels when that happens!
I think it's a play off the old days of Microsoft's blue screen of death. Just dated myself...
This is what we geeks see at the end?
Oh please......... anything but either Wordpress or Microsoft........ please, at the very least be a penguin or little devil............
If I see Microsoft, I know it's not St Peter who I'll be talking to. lol :-)
Hope you are well away from all that terrible flooding in Texas @Muse.
Heart goes out to those folk