DELL SERVER T420 SLOWNESS AND MANY ISSUES

Hi
We are using Dell T420 for which we have replace the Mother Board due to DRAC issue and faced a problem of rebooting suddenly then reinstalled the OS of win 2008R2 standard and then reinstalled all the application we use for our Process that is SQL 2012 for our process ,After the next day of installation i again faced the Problem of rebooting and found the error in the log that "A PCI system error was detected on a component at bus 0 device 31 function 0."and A critical Shutdown below the error After restarting the system I found the System is *** slow and the LAN is not pinging till i disable and enable operation
So I have many problem related to the Server Please help me out for each one
PCI Error ,LAN port access ,System Slowness can any one please help me out on this