Changed Graphics Card ATI Radeon X1900 XT

You don't supply any info: what model Mac was this on? Does this model support the graphics card you installed? If it's in iMac, it will only support what was originally offered including a customizable upgrade. Unless it's a Mac Pro desktop, graphics cards are not meant to be removed or upgraded - only replaced with the same type if defective.

Have you updated the firmware on your MacPro? http://www.macnn.com/articles/07/10/16/ati.radeon.x1900.xt.update/

Oops, I missed the model reference altogether....... apologies to the OP....

From > http://www.everymac.com/systems/apple/mac_pro/faq/mac-pro-default-graphics-cards -dvi-dual-link-mini-displayport.html

looks a little like a downgrade to me - the article doesn't really deal with downgrading to the 'original' MacPro (?wonderng why? - 5770 shot? and X1900 lying around?)

Never tried to downgrade... so I'm out.

ÇÇÇ

X1900 was a poor card, not supported except in 2006/7 (1,1 and 2,1)

Today you would want 5770/5870

http://eshop.macsales.com/Search/Search.cfm?Ntk=Primary&Ns=P_Popularity|1&Ne=500 0&N=7418&Ntt=video+cards

Or AMD 7950/7970 and on Nvidia side, GTX 680 or above.