I have Photoshop CS4 and I need to reinstall it from CD after a computer crash and reinstalling Windows 7 but it won't reinstall I think because it wont fully uninstall. Can anyone help?

Uninstall what you can the normal way thru the control panel then use the CS Cleaner Tool.  Then try reinstalling. You might want to try a download installation rather than the disc if it continues to fail.

Adobe Creative Suite Cleaner Tool

helps resolve installation problems for CS3 thru CS6 and for Creative Cloud

http://www.adobe.com/support/contact/cscleanertool.html

CS4 - http://helpx.adobe.com/creative-suite/kb/cs4-product-downloads.html

You can also download the trial version of the software thru the page linked below and then use your current serial number to activate it.

Be sure to follow the steps outlined in the Note: Very Important Instructions section on the download pages at this site and have cookies enabled in your browser or else the download will not work properly.

CS3 and CS4: http://prodesigntools.com/download-adobe-cs4-and-cs3-free-trials-here.html