I have been having a similar problem. I am running a Sony Vaio RS520 that is about 2 1/2 yrs. old. Earlier this year when I booted up, right after seeing the "SONY" logo, it went to another screen telling me my fan was abnormal. I had the fan changed and it worked fine for a while. But, it started doing the samething again. This time the service tech merely went into the BIOS screen and clicked on "DEFAULT" which stopped this from happening. But, it started up again this past October. (I should note here that just before this first happened I had reformatted my hard drive. This past October, due to a problem caused by software, I couldn't start my computer and again had to reformat my "C" drive. Shortly after both reformats this problem occurred.)
After reformatting I went back to the SONY website to reinstall all the updates that I lost due to reformatting. I am not sure if I had previously updated the BIOS, but I did do so in October. Consequently, the company I have a service contract with won't come out because they claim I reinstalled the BIOS update over the (suspected) previous BIOS update, causing this problem. But, the few people I have talked to tell me that reinstalling the same bios update would cause different, more severe, problems. Also, I should mention, after this last incident in October, I did go into the bios and click on "DEFAULT", but nothing changed.
If anybody has any ideas about what I can do to correct this, I would be very gratefull.