I don't find the MSI 5459 graphics card, William.
Am familiar with the Nvidia GeForce 250 GTS, though.
Using the GeForce GTS 250 as an example, the graphics card requires a 6-pin PCI-Express power cable, for additional power, along with the power it gets from the PCI-Express x16 slot it is in.http://www.playtool.com/pages/psuconnectors/connectors.html#pciexpress
The unit is furnished with an adapter power cable, that converts 2 Molex power cables, (4-pin Peripheral power cables, actually), into 1 PCI-Express 6-pin power cable.
Note that the 6-pin PCI-Express power cable, has two Yellow wires in it.
Let's look at a 4-pin Peripheral power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#peripheral
Note there is one Yellow wire, one Red wire, and two Black wires.
The Red wire is a 5 Volt wire, and not used by the adapter power cable.
The two Black wires are Ground wires, and only one is used by the adapter power cable.
The Yellow wire is a 12 Volt wire, and is used by the adapter power cable.
The 6-pin PCI-Express power cable requires TWO Yellow 12 Volt wires.
(And three Black Ground wires)
This means Two 4-pin Peripheral power cables MUST be used.
Failure to use two 4-pin Peripheral power cables, to that adapter power cable, means the GeForce GS 250 is NOT receiving enough power.
This will burn the connection at the graphics card, burn the adapter power cable connector, and burn the PCI-Express x16 slot it is sitting in.
Takes time, but will happen.
Could this be what you have done?
It also requires 150 Watts all by itself. You need more power for the rest of the computer.
(The 6-pin PCI-Express power cable is designed to provide up to 75 Watts of power. This means 75 Watts of power, also comes from the PCI-Express x16 slot, it is sitting in)
Nvidia GeForce GTS 250,http://techreport.com/articles.x/16504
For additional questions post in a Comment.