Home PC Throwing Tantrum

Reason why there's no post for the past week is due to my PC throwing tantrums. It seems to reboot for no apparent reason. No matter what I do, i.e. reformat hard disk, taking my RAMs for checking at SLS, replacing my PSU, and now replacing my mobo (yet to be confirmed if its the cause).

Now I can't get into the internet as the mobo is w/o LAN port and surprisingly my old LAN card cannot be detected upon installing a fresh copy of Windows XP.... I'm really at my wits end... Hopefully I'm able to dig out the truth in the next few days if not I will be suffering from withdrawal syndrome for not getting online at home...