Do you hear any clicking, or other weird noises at startup? How long do you wait for windows to load before restarting? I'd suggest running this Diagnostic from Western Digital and seeing if your drive fails S.M.A.R.T. protection, that's usually a good indication if it's faulty/going to fail soon, I had one die on me, but that's because I plugged in both the Molex and SATA power connectors at the same time >.<
http://support.wdc.com/download/index.asp?cxml=n&pid=1&swid=3
http://support.wdc.com/download/index.asp?cxml=n&pid=1&swid=3