Computer will not boot

I have a PowerSpec 6342, integrated graphics. If I disconnect the HDD, computer posts. If I connect HDD to mobo using IDE cable with no power, computer POSTS. If I connect HDD to PSU (without connecting IDE cable, computer clicks and immediately shuts off. Tried different HDD, same result. Is it a bad PSU (original) or bad mobo. I also disconnected DVD from PSU and mobo and tried to connect HDD, same result.