ok, here is the 8400gs XP driver page, it looks like a pretty big size file 133mb
download it to a folder you will remember and have it ready to go when you are prompted by windows for the support for the new hardware
ok, when you powered up while the monitor was connected to the card, did you see the compaq splash screen? it only shows up for a second or two, that is your tiny window of time to get into your BIOS/safe mode..i will look up the exact key to use...
ok your presario is f10 to get into BIOS and f8 to get into the boot options and safe mode
prolly the best way to get this component functional is a BIOS reset first....power down the PC and if you look inside the cabinet at the motherboard, you will see a round button cell type battery about the size of a quarter, if at all possible, see if you can dislodge it..then leave it out for quite a while, maybe 30 minutes or so..... put it back in..
if you can't get it out, their might be a another way via the motherboard cmos reset jumper bridge.... but try the battery removal first, it is the easiest way for now.
ok, once you get the battery back in power-up Presario with the card installed and watch for BIOS to prompt you for the time to be entered, if you get that, then your reset was successful. while you are in the BIOS, look for that setting called PEG enable, it might be there, it might not..
after you enter the time, exit and save the BIOS entries and it should put you back into the boot process and see if you can get into safe mode with the f8 key right after you exit the BIOS.
once in safe mode, go to the device manager and look for the display adapter, is it showing up there?
P.S. a BIOS reset is required after you manually power down the machine because your display was blank
Edited by synergy513, 03 September 2015 - 05:03 AM.