If the system was made in 2005.
Add to the fact it`s what we call a pre built system as you say a HP WX 4300.
Your problem and why it revs up with the new graphics card in it.
Is to do with the power supply in the tower based system.
If you look at it the power supply will likely have a wattage rating of 250 to 300 or 350w Maximum.
Your going to need at least a new 500w supply.
Second of all based on what was in the system, or if a graphics card was in the Pci-e based graphics card slot of the motherboard. Or prior to fitting the new graphics card you were using the on board graphics solution of the motherboard.
Then if you look at the motherboard, you should see a connector with four pins on it on the motherboard.
Depending on the PSU it should have the same 4 pin power connector on it.
If it is not connected to the motherboard as it stands. you must connect it.
As it will be required when you fit any Pci-e based graphics card into the Pci-e slot of the motherboard.
If running a more powerful Pci-e based graphics card solution.
Often the four pin extra power from the PSU to the motherboard is not connected if the system is or was using a graphics solution housed on the main motherboard and must be connected when a pci-e based card is fitted to the HP system.
Go have a check if this is the case. Bellow is a link to the HP WX 4300 motherboard, in the picture you can see the connector in white on the board of four pins i have talked about this is where you must connect the extra power from the Psu to the motherboard if you are putting in a Pci-e based graphics card. If not connected it results in the fans revving up and the system freezing or locking.
Click on link to see picture, and power connector on motherboard.
https://www.google.co.uk/search?q=HP+WX+4300.&es_sm=122&source=lnms&tbm=isch&sa=X&ved=0CAgQ_AUoAmoVChMI0fmTy6bIyAIVQkQUCh13lQME&biw=2560&bih=1353#imgrc=zFFHglK7WnGCGM%3A
Should work after that. let me know the results ok. ;-)