some1 downloaded cydia and my iphone doesnt work anymore, the loading is stuck and itunes cant find my iphone ??

Whether you or someone else installed it, or whether you want or don't want it is irrelevant. Support for phones with unauthorized modifications can't be given here, and your warranty is void.

The only thing we can suggest is that your Restore your phone in iTunes as a new iPhone, without using a backup. This may not work and you may get error codes such as 1015, in which case no further assistance can be given.

Instructions for how to backup and restore the device can be found here: http://support.apple.com/kb/HT1414

If you are still unable to restore the device, try this article: http://support.apple.com/kb/HT1808