i have strange problem with prices in magento store. after adding some products in magento backend, almost all products have same price 5,99. Have anyone been in same situation? all help is welcome....
If they're 5.99 in the back-end then I'm afraid you're unlikely going to be able to restore the prices unless you have a backup.
As to why it happend; without knowing the exact actions you took (and without you being able to recreate it over again) it's going to be really hard to debug.
i am new in magento, which extension you would suggest to backup my store and if i need sometime to restor it?
Personally I would not use an extension to do the backups - I would use a mysql dumping tool. Depending on how you access your server there are several ways. Mysqldump if on the command line, of if you use a tool that will have a built in dump feature and also site management tools sometimes have database dumping/backups built in.