Installed new graphics card on HP7 1446s and now monitors are blank

[LinJoh]

I have an HP7 1446s PC. I installed the Geoforce GTX 660 graphics card, but when I powered on, the monitors are blank. I also found out that the onboard graphics card and the installed card will not both work. It is either one or the other. So now I guess I need to disable the on board card. I went into bios, but did not see anywhere to do this. HELP!

 

[Unolocogringo]

Did you upgrade the power supply?
The 660 needs 1 6pin power connector that your original 300watt power supply probably does not have.
300watt is not enough to power the card and computer. Nvidia suggest a 450 watt power supply .
The bios will automatically switch to the PCI-E card when installed.

 

[LinJoh]

Did you upgrade the power supply?
The 660 needs 1 6pin power connector that your original 300watt power supply probably does not have.
300watt is not enough to power the card and computer. Nvidia suggest a 450 watt power supply .
The bios will automatically switch to the PCI-E card when installed.

 

[LinJoh]

Yes, I did upgrade the power supply to 600 watts and I did connect the card to the power supply via the 6 pin connector. I also tried removing the video card, going into windows 8 and disabling the on board graphics adapter, shut down computer, and reinstalling card, but still black screen.

 

[Unolocogringo]

Did you plug the monitor to the graphics card?
Or is it still connected to the motherboard?

 

[LinJoh]

Yes, I had the monitor plugged in the back of the graphics card that I had just installed, not the graphics card on board the mother board.

 

[LinJoh]

Yes I did.

 

[LinJoh]

After two worthless phone calls to HP support (which by the way is located in India), I contacted a very helpful Rep on HP Chat.

Solution: Disable secure boot in the BIOS and enable Legacy boot. Secure boot prevents installation of hardware/software that is not on the "Trusted" list from HP.

See link below to access directions on how to do this. Scroll down for directions for the desktop (directions for laptop is listed first).
http://h20565.www2.hp.com/portal/site/hpsc/template.PAGE/public/kb/docDisplay/?spf_p.tpst=kbDocDisplay&spf_p.prp_kbDocDisplay=wsrp-navigationalState%3DdocId%253Demr_na-c03653226-7%257CdocLocale%253D%257CcalledBy%253D&javax.portlet.begCacheTok=com.vignette.cachetoken&javax.portlet.endCacheTok=com.vignette.cachetoken

Thanks Unolocogringo for the replies above to try to help me with my problem.