HP Pavilion p6774y psu

[aggravader]

I just got a HP Pavilion p6774y and wanted to change the psu but having trouble unscrewing it took out the four screws in the back but it still stuck I'm I missing a hidden screw?

 

[rolli59]

I have ones replaced an HP (model number unknown) PSU for a friend it only had the 4 screws in the back which is the std PSU mount.