Title tag on my template pages missing - cannot switch to default template

I noticed my title tag was missing on all of my catalog pages. Per the forum advice, I 1) checked the metatags switch was on in the admin category types and 2)tried switching back to my default template to see what happens. Well, the default template isn't working... just a blank page with a fine green line at the top. I've attached a picture of the html for that template page. My pica-flor azul template is working fine when I switch back. I just downloaded the complete 1.5.1 zencart to make sure I have all the files but am really nervous about uploading anything before I get a little direction. Thx!

Ok, I finally figured out my settings were incorrect in my easy-populate csv file. Title problem is fixed but I still have no idea why I cannot revert back to the default template. Thx again

When you check the default template (classic), have you checked your log files for an error.

Because you are seeing a green line it would suggest its working (the classic template is a greenish colour I think), but that a template file may be corrupted, your log files should give you an idea of whats wrong