I just got a used Dell Precision 490 with 2GB of memory that didn't have a video card or hard drive. I installed a Seagate Barracuda 7200.7 80 GB drive and a Galaxy Nvidia Geforce 8400GS PCIE 512MB video card. The memory tests OK with Memtest+. I takes over 5 minutes for the BIOS splash (now flashed to A08) to display, and for most of the time the monitor LED doesn't change to green. It's just like it's running about 1/20 speed.
More about :dell precision 490 incredibly slow startup
Other notes: during boot get "Alert! unable to initialize fan controller" - F1 to continue, F2 for setup. I did a very slow install of Windows 7 64 bit - am now going to install Windows XP Pro 64 bit and see if there is a firmware update that will fix the speed problem. Win7 was so slow you could see the initial splash paint - I've never seen a system this slow.
According to Dell's documentation, "Alert! unable to initialize fan controller" might indicate a defective motherboard. Are all fans connected to the motherboard working properly? Since it boots, how fast is the processor running according to CPU-Z?