While trying these other options I would also advise you to check all your cabling to drives. There is a possibility that while installing and uninstalling the NIC you may have unintentionally knocked one of your cables a little off.
From that point it's best to eliminate ALL possibilities.
Disconnect all drive cables but CD and see if you can boot right from there. If no, there is a slight possibility you may have cracked your mobo installing the nic. If it does boot then reattach the HD cable and reinstall OS (as someone already suggested). Could be funky cables, could be weak powersupply, could be screwed HD.. There are as many possibilities as their are parts. As a retired tech the best I can tell you is go from bare bones and add one thing at a time as they work.
Best of luck with it.
