Hello,
assuming we talk about CC, you will find the download page there:
http://www.adobe.com/downloads.html?promoid=JZEFS >>> https://creative.adobe.com/products/photoshop?promoid=KHTUU
Other versions like Photoshop Elements products | 9, 8, 7 for example you can find here
http://helpx.adobe.com/photoshop-elements/kb/photoshop-elements-7-8-9-downloads.html
What concerns the installation problems you could have a look there:
http://helpx.adobe.com/photoshop-elements/getting-started/install-pse.html
http://helpx.adobe.com/photoshop-elements/kb/troubleshoot-installation-photoshop-elements- premiere.html
Hans-Günter