Can't login – connection reset error

I have been using my website for several years with no problems.

Two days ago I went to login and got this error message.

The connection was reset

The connection to the server was reset while the page was loading.
The site could be temporarily unavailable or too busy. Try again in a few moments.
If you are unable to load any pages, check your computer’s network
connection.
If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web.

I have changed nothing on the browser – I use Firefox, have deleted all cookies and caches as suggested but am still getting this error message everytime I try to log in.

I haven’t been able to access my website for 2 days now and seeing as I use it for my business this isn’t good.

Can anyone else help, I see others have had this problem. How have you solved it.

The only thing I did the day before this problem arose was upload a plugin for bublaa – a online forum – so am wondering if this has caused a problem. But seeing as I can’t get into the admin on my account I can’t delete this plugin – what to do?????

Thanks in advance
Helen