What card did you have in it before  ?  If it was a nVidia card, did you uninstall the old driver, use a driver cleaner, than install the new card, and new driver ?   Did you install the molex Y cable from the back of the video card to a power connector on your system  ?

Proper install of a video card :

Download the most current driver, and have it placed on the desktop for later install.  

Going from an ATI card to NVIDIA or vs. versa, one should uninstall the old driver, from Add/Remove program.

Use a driver cleaner, to get all the old  driver code completely off the system.  Use the driver cleaner twice. 

http://www.hardforum.com/showthread.php?t=752253       Information as to how and why you should use a driver cleaner 

http://www.drivercleaner.net/        Driver Cleaner Pro download site

Turn off the system, unplug the power cord, push in on the systems power button, to discharge the system further. 

Remove the old card, and install the new card, firmly.  Attach any power cable to the card, and to a power connector if required.

Plug the power cable back in, and reboot the system.  You will notice that the monitor screen is larger now.  Not to worry.

Install the newer video card driver from the desktop, than if necessary go into the Display Properties to reset the monitor resolution.   You are now done….

http://www.newegg.com/Product/Showimage.asp?Mode=&Type=&Image=14-102-678-02.jpg%2C14-102-678-03.jpg%2C14-102-678-04.jpg%2C14-102-678-05.jpg%2C14-102-678-06.jpg&CurImage=14-102-678-05.jpg&Description=ATI+100-437510+Radeon+X1600PRO+512MB+GDDR2+AGP+4X%2F8X+Video+Card+-+Retail   Look at this link and you will see the molex power Y cable on the right side.  Did you install the power Y cable by chance  ?

Message Edited by SR45 on 04-08-200604:22 PM

Did the solution work for you?  I am having the same problem.  Trying to upgrade from an nVidia card to a Radeon x1300Pro graphics card.  Having the EXACT same issue with the blank screen, but no problems after I put the old video card back in.  I have not updated my BIOS (how do you do that anyway and is it necessary?), but I have run the driver cleaner and uninstalled all my old nVidia drivers.  At least I think I have.  Nothing shows up on a dxdiag analysis.  But my opening screen when I boot up with the old card does still show an nVidia card in the opening text that shows up initially for about 3 seconds.  I'm so frustrated!!!  If you get your Dell 4550 working with the new Radeon card, please let me know on this posting or email me at dhu4@nyc.rr.com.  Also, I don't believe our cards need the y mole connector for power.  I think our motherboards supply power to the Radeon.  I may be wrong, though.  Do we have to do anything with our motherboads maybe?  Our machines are a little old.  Thanks to anyone who can help!

Thank you very much for your assistance. Yes i am going from a nVidia to an ATI, but i still havent had any luck using the methods described above. i followed them EXACTLY and still nothing when i boot up my computer. im beginning to think my card is bad. i would rather not take it back though. if there is any other advice anyone can give, it would be greatly appreciated.

BTW...if i somehow manage to get this card working, ill be sure to let you know Den1020 :)

Thanks, Funky!  I'm having the same bad luck.  I think I'm going to take the ATI card back and just upgrade with another nVidia card.  This is actually quite ridiculous.  Graphics cards are supposed to be so easy to install.  And Dell computers are usually pretty compatible and easily upgraded and accessible for the "insides".  Good luck, and I'll still be interested to hear of any success you may end up having.

well, it seems that i had a bad card... just getting someone to tell me that was like pulling teeth. so i sent back the old card and upgraded with a nivida as well, just to be sure.
:P
Thanks to all for the help!!!!