Help Apps not Installing

[An UrgeTo Dance]

Okay so my phone is not installing any apps, when I tell it to install it downloads it completely then it will not install it, it says installation failed. I have restarted my phone twice and tried to install over 3g and using the WiFis and it still is not installing I know I have enough room on the phone because I even went and deleted things off of it thinking that may be the issue but it is still not installing. Any one else having this problem, or know how to fix it if so please help me. My phone is not rooted and is running FroYo.

Thanks,
An UrgeTo Dance