The reason could be that your computer is experiencing an IRQ (Interrupt Request) conflict, meaning, after the network adapter was physically installed in your computer it may have been assigned an IRQ that was already in use by another device. PCI cards can share IRQs for the most part, however, network adapters usually cause conflicts when sharing IRQs with other devices.
The network adapter and the other device both try to get the attention or "interrupt" the processor (CPU) at the same time. This "confuses" the processor, and may cause it to lock up (freeze) or keep the computer from booting all the way up.
The simplest way to try to fix this problem is to shut down your computer, unplug the power cord and move the network adapter to a different, available slot inside your computer.
Reconnect the power cable to your computer and restart.