law turn your pc off...make sure there no power to the mb and check that your ram and power cables are connected. make sure there no dust clogs and that your fans are moving. on your new drive did you clone it or do a clean reinstall.
on a clean install some of the newer drives you have to run some tools because new drive use a newer partioning that xp does not like. http://www.hgst.com/hard-drives/advanced-format-drives
the next issue could be a bad stick of ram. make a memtest86 boot disk and run it over night.