el capitan upgrade

[nanpera]

After upgrading to El Capitan I can not open PSE nor can I paste anything to my Seagate external hard drives.

 

[mzd]

Assuming PSE is Photoshop Elements, then you probably need to download Java from Apple here:
https://support.apple.com/kb/DL1572?locale=en_US

not sure what to tell you about writing to the Seagate drive.