Create account and contact forms not working

Hi,
Had our site running on v139h for ages.
Just discovered that for the last 4 days, people can't create an account or send using the contact us form.
Once filled out, the page just has the browser loading icon and stays there with the form still on screen. (no blank pages)
Perhaps something with the host as its on all 3 of our zen-cart sites? Any ideas?
Sample: Website

Thanks...

If they worked before and suddenly are not working I'd be asking my host what they changed.

Thanks Kim, pretty sure it was the case but thought I'd check while I wait for the weekend to be over so I could contact them. (money not coming in and all)
Appreciate the confirmation.

Kim:

If they worked before and suddenly are not working I'd be asking my host what they changed.
Host has just told me that nothing has changed and nothing they can do without paying for their support.
I can't find anything by searching anywhere, so if anyone can tell me where they would start?
I cleaned out the debug files before realising there was an issue, however as it's all 3 zen-cart sites (same hosting) I assume it's a database issue and nothing new has popped up in debug.
Would reinstalling fix such an issue?
Appreciate any help as I'm lost and going broke...

Are you getting any email through the accounts those sites use?

Kim:

Are you getting any email through the accounts those sites use?
Yes, if sent directly they come through fine.
We can also create orders through admin using existing customers accounts, so guess that suggests 'most'of the database is ok?
Thanks Kim

If I'm getting this problem on 4 zen-cart sites, can I rule out zen-cart as the problem? Should I look to phpmyadmin (not that I'd know what to do)
Host has 'checked' and said no issues with them.
Freaking out here...

Did the forms work before?

Kim:

Did the forms work before?
Yes, all worked for the last few years with all zen versions that we've had.
Have tried default template just in case, but no luck...

If they worked before and you haven't changed anything, then keep yelling at your host.

So host simply blames it on bad code (5 sites? 3 of which haven't been modified in months)
Have changed host today.

While I wait for domain name to propagate so I can view my new default zen install, I have one question please.

The tutorial for moving database to new host states to use the same prefix in database, as the old site had.
My old hosting had 10 sites, so they had their own prefix eg: this_siteone and this_sitetwo
The new host defaults to eg: that_ so can't use same prefix?

Any one know better? Thanks

The "prefix" that the Tutorial is referring to is the DB_PREFIX in your configure.php files. This prefix is used by Zen Cart to identify groups of similarly-named tables INside your database.
It is NOT referring to words/letters used in naming your database.

Thanks for that Dr.