Update your BIOS using the recovery method (since you're unable to use your keyboard). There's a blurb about not being able to use a USB keyboard to enter the BIOS under BIOS 0112 in the BIOS release notes http://http://downloadmirror.intel.com/18047/eng/SG_0121_ReleaseNotes.pdf
2. BIOS Recovery Instructions: http://www.intel.com/support/motherboards/desktop/sb/CS-023360.htm I typically use a CD.
3. Here's a diagram of your board, and it shows the location of the BIOS configuration jumper, which needs to be removed for a BIOS recovery: http://download.intel.com/support/motherboards/desktop/dp45sg/sb/dp45sg_configlabel.pdf
4. When that's all done, check your boot order...
Intel Boot Agent GE
PXE 61 Media test failure, check cable
PXE M0F Exiting Intel Boot Agent
means that your computer is booting to network, either because it is first in the boot order menu, or because you have no other bootable device.