This was a curious and frustrating problem to fix. After updating the local dev copy of a a magento site, and changing a few local folder permissions the admin area stopped working, giving instead an error message of: ERROR_CONNECTION_RESET.
Now my local development system was, in this case, a Windows 7 machine running WAMP 64. In order to run some scripts I had recently modified some folder permissions with cygwin. This may well have caused the problem but I did not discover this until a while later as a raft of data updates had been running for some time.
Having puzzled about why the connection was apparently being reset I discovered that the front end of the site was working fine. This lead me to believe that the error was down to something else other than the connection.
I checked the WAMP php error log and indeed, aside from a few dynamic library load warnings I spotted a load of permission denied errors on session files located within /var/session/ . On checking this folder I noted that all the permissions had gone screwy on that folder. I cleared it out, reset the windows permissions and reset ownership to myself (via the properties->security tab) and bingo – the log in screen thankfully reappeared and I got through.
Don’t always believe the error messages. Check the error or exception log (can do this for WAMP via the tray-icon > PHP ).