permissions – can’t access admin

I posted this in another thread and I think maybe nobody’s noticed it and I’m on the verge of tears, really, I desperately need to get into my WP blog and have been trying for about 10 hours and I’ve tried everything I can think of.

The problem: When I try to login, after putting in correct usr name and pass I get the message:
You do not have sufficient permissions to access this page.

But if I use the back button to go to the blog, not logged in, the one any reader would see, and refresh, the Site Admin button is activated instead of the Login button, so actually I am logged in, WP just won’t let me see the admin interface.

I’ve worked through the troubleshooting tips here:
http://codex.wordpress.org/Login_Trouble

– deleted cookies
– deleted plug-ins
– replaced wp-login.php (in fact upgraded entirely to v2.5)
– reset password at least three times
– did NOT edit Users Table as this is not really a password problem, the password works, its the permissions)
– checked siteurl and home in the db – they are properly configured and there’s no “If someone has moved WordPress…” in the config file
– the site is not within a https:// domain
– I don’t know from firewalls; but I use Windows XP and Norton Anti-virus; my internet provider, Rogers.com may have firewalls but I also have another WP blog on the same server, running v2 and it’s fine so I don’t think that’s it
– I also asked my host, Pair.com, to check the permissions and they said they are all normal and told me to consult with WP

So here I am. I have read all the many many posts on this topic and am sorry to be asking yet again but I’ve done everything I can think of…

oh one other thing, I recall coming across a post on this topic that suggested that maybe the latest upgrade of Firefox possibly created this problem but I’ve tried IE and installed Opera and still the problem persists.

There is an .htaccess file in the root directory… perhaps that’s where the problem is?