Looking for new GPU + PSU

[Inumayobaka]

I am having some problem with my GPU.
When I turn on my computer, my screen remain blank.
Plugging the monitor to my on board graphics detects the system.
I intend to get a new GPU but it might require a new PSU.
Anyone out there who could offer me a reasonable price for both?
Unless you think my PSU can handle the GPU you recommend...
This is my current PSU. Cooler Master: Thunder M 620W
This is my current GPU. Radeon HD 7850.
I do not mind a second hand GPU as I am only looking to replace this current one. I bought it for about $300 previously.
I am only concerned about my PSU being able to handle the new GPU.

 

[cenedra]

my 620w seasonic can handle my overclocked i2500k + overclocked R9 290 + 1 SSD + 2 HDD. The R9 290 requires alot more power than ur 7850, somemore i overclocked it and my CPU.

Add: Prior to getting the R9 290, i was running a 7850 with a 500w silverstone PSU. That PSU dont have a 8 pin connector for my R9 290, thats why i buy a new PSU.

 

[Alphas]

I am running sli 670gtx x2 i5 with 3hdd and 2 ssd on cm 620w psu, u say then?