can't get subscriptions working

I've become stuck.
I created several subscriptions while getting used to the software and made a test payment thru paypal solo and all went well.
I went on to create some new subscriptions and, when out of admin, I tried to click the paypal button and nothing happened. (small square box next to paypal logo not present).
So, I cleared all test subscribers - also checked on MYSql - and deleted all subscriptions hoping for a fresh start. Activated and made public,
Created just one and the problem persists.
Please help - running out of steam
Can be seen at http://www.brandsponsor.co.uk

Thanks, Ben