GPU powers on but no display

[pututski00]

So the situation here is I have a cheap OEM Lenovo thinkcentre m90p that I wanted to throw a GPU into to see if it'll run any games. I got an AMD r7 250 low profile, and it fits perfectly fine in the computer! However, when I run it with the GPU in the you fan will spin up as will all the other components but will not display the graphics from the displayport on the GPU. I wonder if it's due to the GPU not getting enough power (it's only a 240w PSU) or if it's perhaps something else like just the displayport (have not tried the DVI)

What I have done so far:
- turned off integrated Intel HD graphics
- installed GPU drivers
- went into bios and set PCIe to priority for video display output
- bought brand new displayport to HDMI cable

I don't get why there is nothing even displaying on the screen even though all components seem to be working totally fine. I believe it could be the PSU

 

[Calvin7]

System Requirement 400 Watt Power Supply (Suggestion)
http://www.sapphiretech.com/productdetial.asp?pid=B4DBE4FA-071A-4291-B92E-F4434BD796FA&lang=eng

 

[pututski00]

Tested the GPU in my normal system, runs perfect. Seems to be just not enough power for it. Thanks!