Your system is trying to boot from the network/NIC.
Go into the BIOS and set the proper boot option (hard drive first).
On some motherboards/systems, this may be a default setting or an indication that the CMOS battery is weakening and needs to be replaced (costs less than $5).
CMOS Battery Replacement - http://www.liverepair.com/encyclopedia/art...cmosreplace.asp
If you replace the battery, be sure to enter the BIOS and adjust date/time after doing so.