Why not just run the server on the raspberry pi? An idea you could try is to run a ftp server on the raspberry and a samba server on the other computer.
On the raspberry have your main ftp directory as /samba. Then when the main computer turns on your samba server will start and thats where you files will be pulled from.
Just have a ftp banner saying refresh in 30 seconds. Then write a bash script to monitor the connection log. When someone connects it checks to see if the server is on if not it runs your power on command which will then start you samba server.
You could do all this with bash.