SRX210 Booting from backup image 10.0R3.10

Rank amateur alert!

I have a spare SRX210 which is booting from the backup image. It had previously been ok but i think a sudden power outage killed it. I want to be able to put the latest software on but following the GUI instruction in this article

http://www.juniper.net/techpubs/en_US/junos14.1/topics/example/security-junos-os-upgrade-srx-series-device-installing.html

the procedure hangs after i click 'Upload and install package' - I'm trying to install version 11.4R9.4 but i read somewhere on these forums that you can only go up in smaller upgrade steps.Eh 10.0 to 10.4 then 10.4 to 11.4 but I can't find the download for 10.4 anywhere.

any advice greatly apreciated.