Can't log on to my admin page, get browser download dialog instead

Have you tried:
-deactivating ALL plugins temporarily to see if this resolves the problem. If this works, re-activate them individually (one-by-one) to find the problematic plugin(s). If you can’t get into your admin dashboard, try deactivating via FTP or SFTP or whatever file management application your host provides. If applicible, also remember to deactivate any plugins in the mu-plugins folder. The easiest way is to rename that folder to mu-plugins-old.
– To rule out any theme-specific issue, try switching to the unedited default theme for a moment using the WP dashboard. If you don’t have access to your admin area, you can switch to the default theme by renaming your current theme’s folder in wp-content/themes and adding “-old” to the end of the folder name using via FTP or SFTP or whatever file management application your host provides. Alternately, you can remove other themes except the default theme. That will force your site to use it.
– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems (because the hooks remain unless plugins completely removed or some plugins stick around in cached files. So by renaming the folder, you break them and force them inactive).

I’m sorry, pretty much everything you’ve suggested goes totally over my head. I use no plug-ins; my theme is, “WP Comic” run pretty much out of the box. I’m going to have to try the steps you suggested via ftp as I’m unable to access my dashboard.

This has apparently just happened as of the time of my original post; I posted a fresh entry less than 24 hours ago, and my dashboard and blog were functioning perfectly. I discovered this malfunction when attempting to log onto my dashboard to download my XML site backup. I haven’t attempted any fancy tweaking; the only changes I made in the past couple of days has been to reset my last few posts to not allow pingbacks or trackbacks — I have comments, pingbacks and trackbacks switched off globally — because of a rash of trackback spam last week.

They basic troubleshooting steps. Read my post again.

OK, will do. Diving into ftp now…

OK, I’m in ftp now.

I can’t find a mu-plugins folder — assuming I’m in the right place — so I’m assuming I have no plugins running.

Deleting unused themes and adding “-old” to the name of my current theme’s folder name doesn’t work.

Renaming the plugins folder to “plugins.hold” doesn’t work.

Here’s another bit of info that might help: out of curiosity, I tried to access my blog using my wife’s laptop, which runs a later version of Firefox, and received a “500 Internal Server Error” message in the browser.

I’ve just done some Googling for the WordPress “500 Server Error” issue, and it’s apparently due to too many connections. Could this have something to do with the brute-force attack issue reported here recently?

A lot of things can cause 500 Sever Errors – ask your hosting company how to look at the error logs for your site – that should provide some more info.

Thanks; they’ve been contacted.

I’ve also found some earlier posts on this forum which suggest that a corrupt .htaccess file might be involved. One of the people at my hosting outfit replaced it a little over a year ago with one containing some commands customized for WordPress after they’d done some adjustments to something called “mod security” to prevent it blocking my ability to post to my blog and generating a “406” error.