X51 issue "reboot and select proper boot device or insert boot media in selected boot device and press a key"

Hi Burningfenix, that could be a number of things but probably best to check the basic first.

Have you checked to make sure the cables are connected to the hard drive and motherboard, they may have come loose while you were changing the GPU?

When you bootup the machine, hit the F2 key and go into the system BIOS and scroll arcoss until you get to the option "Load setup defaults" or something very similar, reset the system to the factory setting. Before exiting check to make sure that the reset has not changed the sata operation to RAID, it should say AHCI or UEFI depending on what BIOS version you have. Save changes and exit, your system should boot up automatically and hopefully with no problems.

If you still have no luck try booting up again, hit F2 again and change the default video card from "discrete" to "integrated", save changes and exit.

This will possibly tell you if the new video card is causing the problems, hopefully it will also allow you to access windows and from there you can update your system BIOS, I think the current X51 system BIOS is upto A13, so check your version and see if it needs updating, the BIOS version number will be directly under the alienhead logo you see when the system starts up, this is also probably one of the first things Dell tech support will get you to do if it is still under warranty.

I dont know if this will make a difference but also check to make sure the video power cable you used is labeled number 1

Keep the posts coming, theres heaps of people on here who can help you, if you can give more detail on your machine and the video card you installed, that would help too

Goodluck

Hey there, so I managed to fix it but not sure if it was a fluke or not. I read somewhere in yahoo answers that someone unplugged the power cable from their computer and pressed the power on button for 5 seconds for a total of 3 times then waited 2 minutes and plugged everything back in. I tried that and once I went back into my boot menu I set HD to number one and it worked. Not sure if that was coincidence or not. Video card is working fine! Thanks for your suggested answer though!

what you did was a FULL power drain of the power  board and motherboard.  Basically resets them and cleared out the issue you experienced.

I could kiss you right now I've had so many problems trying to get in contact with dell etc but I thought I might try what you said and bingo!! Worked a treat, thank you so so so so so much

We'll HELP ME THERE NO LEGACY OR UEFI BOOT OPTION

This issue happened after the A10 upgrade and this fix worked. Thanks!