Putting a graphics card in a motherboard that doesnt have a 24 pin connector for a higher psu.

Solution
That model of PC uses proprietary parts. The motherboard doesn't use standard ATX power supply connections. The HD 7790 is not a supported part for that model. You may want to buy a bare PC case and different motherboard to use a HD 7790.

These are the two power supplies that are available for your HP PC.
#508153-001
Power supply 320 Watts standard - For Microtower PCs --$ 147.77
#508154-001
Power supply 320 Watts - Has 89% efficient rating, wide-ranging, Active Power Factor Correction PFC technology - For Microtower PCs -- $ 191.93
That model of PC uses proprietary parts. The motherboard doesn't use standard ATX power supply connections. The HD 7790 is not a supported part for that model. You may want to buy a bare PC case and different motherboard to use a HD 7790.

These are the two power supplies that are available for your HP PC.
#508153-001
Power supply 320 Watts standard - For Microtower PCs --$ 147.77
#508154-001
Power supply 320 Watts - Has 89% efficient rating, wide-ranging, Active Power Factor Correction PFC technology - For Microtower PCs -- $ 191.93
 
Solution