Please look at that guide, as it'll walk you through how to find error messages in DSpace 7.x (which will provide you with more information about what is going on in your installation).
Also, please look at our Common Installation problems here:
My best guess is that you may have a configuration error in your installation which is causing those problems. However, if you follow those two guides, you'll likely be able to locate a more specific error message and/or find the fix yourself.
Let us know how it goes.
Tim