My computer is an HP HPE H8 1234 and I just replaced it's AMD HD 7450 with a Zotac Nvidia GT 640 GDDR5 2GB and when I boot, it just freezes at the HP screen and it says "press esc to access menu" or something like that.
I installed the graphics card correctly but I don't know what's going on.
Does the computer boot normally when you re-install your old GPU? My guess would be the junk PSU can't provide enough power for the new GPU. It's a 300W PSU and the minimum recommended PSU wattage for your new card is 350W.
I wouldn't make any assumptions in regards to the low quality PSUs OEM builders use in their machines. They are barely up to the task of powering the stock system. All bets are off when performing an upgrade. Did you try the old GPU to see if the system boots? If so I stick to my theory that the PSU can't provide the needed power for the new card.
I tried going into Device Manager and uninstalling the AMD drivers in the Display Adapters section. Is that wrong? I uninstalled the drivers that way...
Should i uninstall the Catalyst Control Center instead?
The GT 640 should work with just about any OEM PSU. It is only a 65W card. And then only when maxed out. During boot it is practically at idle.
I would go to Control Panel/Programs and Features and
1) Use the Catalyst Control Center to uninstall all the AMD stuff.
2) Then go to the Nvidia stuff and uninstall all of it