Is it wireless? It might not be getting a good connection. Try moving your computer closer to your router and see if it works better. Perhaps you don't have enuogh power to supply the to card the from your PSU. How many watts is that?
Did you get the updated drivers? (you never know it might not like something in your new system)
Is everything totally connected properly? Stupid question, but sometimes people make mistakes
Try another PCI slot. The mobo might not be working perfectly.
Do you have any integrated LAN on your mobo? Perhaps its conflicting.
Just a few little checks you could try out... Good luck
Sometimes the only way over a wall is to pile up enough bodies to climb over - Dave W.