Photoshop 7.0 reinstall without disc

I had to uninstall my Photoshop 7.0 because I was getting the following message when I tried to open it "C:\Program Files\Adobe\Photoshop 7.0|Photoshop.exe is not a valid Win32 application". Now I would like to try to reinstall it to see if it will work, but I don't have a disc. I do have the serial number. I did not receive any disc with my computer. I did receive a paper from Dell that says "Your new computer does not require an operating sytem CD or drivers CDs. Instead, if you ever need to reinstall your software, use one of the following methods." One of the options is "Microsoft Window System Restore", the other option is "Dell PC Restore". All I want to deal with is the Photoshop issue. So all that background information just for me to ask if anyone knows how to reinstall Photoshop when I don't have a disc but do have a serial number?