WordPress post/update issue!

Hello,
I get a issue with my wordpress fresh install!
I have a wordpress theme installed and wp-ecommenrce plugin and i get this issue:
When i add a product to a category to store its take too long to post and after i get a blank page. After, when i try to load the wordpress site i get the issue like connection time out or something like that. After some time when i tryed again to load the site its working and the product which i have added it`s appear to the store!
When i try to make some changes to the product and try to update i get again black page or connection time out or something like that and the site dosn`t work again when i try to load it!

Conclusion: The site when i try to load after i post or update a product dosn`t work, but only after when i post or update a product to store!

It is because i set a very strong and long MySQL database name with small/caps lock and number and to the MySQL username too with small/caps lock and number too!

I ask you this because i installed the theme like a test to other domain on some server with a very weak MySQL database name/username and password and it`s working very fast and easy!

I dont understand why on a place its working fine and in other not!
I mention that i have only wp-ecommerce plugin installed and not more!

Can some help me to understanding what is the problem and to fix it?

Thank you!

All The Best!