I am a victim of such problem and thinking I am the one and only victim(Cause can't find any solution or topic with Googling).....
I am still signed in here from my PC,Never log out till today and have no problem with PC access but whenever i go to sign in through mobile after putting name and password the page reloads but again the sign in page comes and it happens again and again,at last I CANT SIGN IN.
My mobile is very old and cheap(SAMSUNG J150 b) but have EDGE feature and have no problem accessing facebook,orkut but have only problem here.
TH doesn't do very well on mobile devices unfortunately, so you're not the only one with the problem. From personal experience it doesn't work well on Blackberries, as the sign in box will not even appear. I've also heard that it doesn't work well on ipads and other tablets. You may have better luck with a newer phone like something with android that is able to handle script and such better.
As Kevin said,TH doesn't play very well with either mobiles and tablets.I tried signing in with iPhone/iPad and it worked fine but overall the experience wasn't so great(compared to PC).So getting a new phone will definitely help but still won't be perfect
my pc's gone for repairs. So i'm posting this message from my mobile. I had this similar problem at first. but i kept trying and i was signed in. now, i don't log out in fear that i won't be able to login again. i have a samsung wave gt 533.
We're making strides in optimizing and modernizing our site a bit better as of late with the new homepage on its way. We'll be shifting over to focus more on usability in mobility at some point as well.