There are adapter cables for 4-pin Molex to 15-pin power needed for SATA drives, They should be $2 or less, but a computer store will try to gouge you.
A newer power supply will come with at least one SATA power connectos
The only problem with the power adapter cable is that the only power connected to the hard drive is +5 volts (red wire) and +12 volts (yellow wire). Without the +3.3 volt input (orange wire), no S.M.A.R.T. data will be reported to the motherboard. By the way - you'll be happier if you use a latching SATA data cable. I have power adapter cables I'll never use, but there's no way to get one to you. Don't get gouged!