Is my mobo now faulty?

I upgraded my PC and used my old components to build another PC in an old case I have.

Everything seemed to be fine up to the point where all of a sudden my LAN controller disappeared from Windows. No lights are flashing on the port whether it's booting up or in Windows itself.

As a temporary measure I installed a wireless dongle which works but after about 1 minute into booting Windows it disappears with the usual message about the USB port being able to perform faster etc. The dongle eventually comes back to life. In fact, I also get this with any USB device. I have installed the latest drivers although can no longer with the LAN controller as it can't find it anymore.

I tried to reinstall the OS via USB flash drive but states a system disk error instead although this drive works fine on other PCs.

Not only that the monitor shows only half the screen when booting into the BIOS. It does show the full screen after resetting the CMOS but reverts back to shite after a reboot.

Is there anything else I can try before I give it the last rites? I've got a feeling I must have shorted something against the case or it had a spazzy fit when it realised it was no longer my main PC!

Thanks very much and hope you can help.