Your computer might have a newer version of PCI-Express*. The adapter you have was designed for PCI Express 1.0a and can keep some newer computers from booting. If that is your issue, newer quad port adapters are compatible. The Intel® Gigabit ET Quad Port Server Adapter, E1G44ET, is designed for PCI Express 2.0 and is your best choice for a quad port adapter.
The Intel® PRO/1000 PT Quad Port Low Profile Server Adapter, EXPI9404PTL or XPI9404PTLBLK is designed for PCI Express 1.0a, but is compatible with version 2.0, so you could use this adapter.
Another possibility would be a lack of system resources causing the computer to reboot. I have run into instances where I could not boot a server after adding another adapter unitl I changed BIOS settings to disable adapter PCI options. I cannot remember the exact BIOS setting description. This might be the configuration options that the others were talking about.
I hope this helps.