GPU not working often

[retroreactor]

I recently brought Sapphire HD 7750 and found that my PC doesn't inputs from it sometime rather it takes from onboard. my mobo has auto disable onboard as I've experienced it.

I checked my pcie slot by inserting my old 210 and it works perfectly.

Also card is fine as when it worked I played fc3 and hma.

my specs are -
Intel Core 2 Duo - E4500 2.2ghz
Ram - 2gb x 1 , 1gb x 1 ddr2
mobo is stock one of Lenovo K200, I don't know its model no.
Psu is also stock 450W
Hdd - 1x 250Gb Hitachi, 1x 1TB Seagate Barracuda
No optical drive or modem card.
1x 90mm Cabinet fan , Deepcool GammaArcher 120mm CPU fan.

I'm guessing here that psu or mobo is insufficient anyway I wanted to confirm as I can only invest in one of them atm. thanks

 

[sanilmahambre]

I dont see any reason why the card is not working since you have properly installed the card in your PCI E X 16 slot.
=> Make sure you are using the DVI or HDMI or Display port on graphic card and not mobo.
=> Check the interface cable for damage or cuts
=> Install the catalyst drivers from the CD or download them from AMD's website
=> You are having a 450W PSU so that is not the issue for sure since it is having a minimum requirement of 400W PSU

Follow this footsteps and right click on desktop and you'll see a catalyst option at the top..click on that and if catalyst manager opens then you are done!!!!

BEST OF LUCK