Alienware M11x shuts down randomly

I have a M11x laptop and made the mistake of trying to install Linux alongside Windows 7 on it.  Linux installed but then Windows 7 wrote over the MBR and rendered the laptop unbootable, so I had to reinstall Windows 7 and all the Alienware drivers I downloaded from dell.com.

A few days ago, the laptop started shutting down randomly during use.  It had been working without any problems until then, so perhaps this is a hardware issue, I don't know.

I believe I voided the warranty by installing Linux and so I don't have the option of returning the laptop for repair or exchange..  Does anyone know what could be causing this problem and how I might fix it?  I thought it might be the Nvidia drivers, so I upgraded them but they did not work well so I rolled them back to the ones Dell has for download for this laptop model.  This did not solve the problem of the laptop shutting down.  I am not sure how to restart it.  I can't always restart it easily.

When I do get the laptop restarted, which I just did by removing the external power, the date is rolled back to January 5 2010, almost every time.  The problem might be the power supply but I don't want to buy a new one until I am certain of this.  I have restarted the laptop in the past after removing external power, then reinserting the plug.