Bought a new processor for my Alienware x51, now it won't boot up

[Laserhole]

So I bought an Intel i7 4790k last week for my Alienware x51 R2 and it came in yesterday. I thought I installed it correctly but when I turned on the computer I heard some beeping and the monitors wouldn't display anything. So I took the case off and I found out that the thermal paste on the fan had not been touched. I put my old processor back in and it beeped, then shut off. Then it kept on restarting. Please help. I think I may have fried my motherboard but I also may have not installed the processor right. I don't think the fan or heat sink was installed right. I already check pretty much everywhere and the Alienware x51 is supposed to be compatible with the Intel i7 4790k. I know I have the right socket too (1150). I don't know what to do at this point. Any help would be appreciated. I will answer any questions you need asked to the best of my ability.

 

[James Mason]

Did you update the BIOS first before installing the new CPU?

Did you make sure to line up the golden arrow on the CPU with the notched arrow on the motherboard socket?

 

[Laserhole]

I didn't know that I had to update the BIOS, but I did align the notches. What do you recommend that I do now?

 

[James Mason]

Put your old CPU back in if it isn't.
replace the thermal past on the heatsink/fan (you basically have to everytime you take it off)
http://pcpartpicker.com/part/noctua-thermal-paste-nth1

Did you unplug any cables and not plug them back in? the CPU/heatsink fan? There's a specifc pin for it on the motherboard that the motherboard checks to see if it's plugged in.

BUT, if everything is hooked up correctly and it gives 1 beep you may have damaged your motherboard.
http://www.dell.com/support/article/us/en/19/496582/en?c=us&s=dhs&cs=19&l=en

 

[Laserhole]

Ok, I just checked out the second page you linked. Quick question: Is it possible that I can use the new processor (Intel i7 4790k) with my motherboard or did I damage it permanently so I will need to buy a new MB? Yesterday when I used my old processor and it beeped once then shut down.

 

[James Mason]

Ok, I just checked out the second page you linked. Quick question: Is it possible that I can use the new processor (Intel i7 4790k) with my motherboard or did I damage it permanently so I will need to buy a new MB? Yesterday when I used my old processor and it beeped once then shut down.

It depends on what motherboard you have, I don't know what one you'd have, as there's probably multiple configs and model years on the x51.

In theory any 1150 socket capable motherboard could run an i7-4790k, but it may be your PSU doesn't supply enough power to power one.

What CPU did you have before?