Photoshop 4.0 is not compatible with MAC 10.9.3 . You will face issues as when Photoshop 4.0 was launched there was no MAC Mavericks and Adobe has not tested the version on new MAC OS.
If you want you can download the latest version of Photoshop CC 2014 and you can use it as a trial for 30 days and you can plan to switch to the latest version.