Your PSU looks...frightful.
I'd say 500-600w, but it might work, if your lucky. Have fun trying to upgrade. Everything else looks sound.
PROTIP: Total wattage isn't the thing that matters the most when choosing a powersupply.A lower watt PSU from a quality brand (Corsair, Silverstone, Antec) will actually perform better than a PSU from a cheapo manufacturer (too loving many to name).
Amperage and the quality of the power (less interference) provided is more important.
The Corsair 400CX to have plenty of amperage left over for more powerful CPUs or GPUs.