CMOS stands for (and no one needs to remember what it stands for) Complementary Metal Oxide Semiconductor or Substrate. But what it's important for is this:
The term refers to the contents of a CMOS chip on the motherboard, which holds information about the system and its peripherals even while the system is turned off.
So, it's what "remembers" things on your motherboard and your peripherals even when you shutdown the pc. All of the information in your "Setup" or "Bios" is stored there. You know; the info when you first turn the pc on about "Detecting Hard Disk", etc.
Sometimes the Setup or Bios gets corrupted or kind of just gets stuck. The only way to reset it (for our purposes, the only way) is to remove the circular shiny battery that's located on your motherboard. It's about the size of a quarter. That's what provides the power to the CMOS/Bios when the computer is shut down.
So, first do this: Unplug the pc from the wall AC outlet. Now, find the battery on your motherboard. It's silver. Make a note on which side has the "+" symbol and which side had the "-" symbol before you take it out, so you replace it the same way.
Take it out (again, with the pc unplugged), and leave it out for 15-20 minutes to ensure that all power and info has drained from the CMOS chip.
Look on the motherboard for text labeled "ClearCMOS" or "CLR CMOS" or similar. (Note: it would be helpful if you posted the exact model of this Sony computer!). Next to that wording you should see a plastic piece, probably black but could be white, that's covering two out of three metal pins sticking up from the board. In it's normal position, it's probably covering pins (metal vertical pins) 1 and 2. To clear the CMOS info, you will need to move the plastic piece, aka "jumper", to pins 2 and 3 instead.
Do NOT haphazardly find any jumper piece and move it. You probably have more than one jumper on your motherboard. Make sure it's the Clear CMOS jumper. Your computer manual should have a diagram showing you the location of this jumper. Again, please post the model of your Sony here.
After 15-20 minutes, move the jumper plastic piece back to pins 1 and 2.
Then, put the battery back in and plug in the pc and boot up. The Setup/Bios will probably give an error message about loading defaults or something, but it may not. In any event, it should go then and do a fresh redetect of information about your system.
Edit: By the way, a search of the "Hardware Monitor has found an error" resulted in this comment, translated from Japanese:
"This phenomenon, when heat inside the VAIO frame exceeds fixed temperature, or [ PWR-FAN ] occurs when the cable which is connected to the connector has come off."
So, look for the connector on your motherboard labeled "PWR-FAN", and make sure it's properly connected to its associated wiring. EVEN IF THE FAN IS RUNNING, MAKE SURE TO RESEAT THE CONNECTOR. Flying Penguin posted this possibility above, and I haven't seen you respond to it.
Sony's American/English page gives this general response to a hardware monitor error. Note the word NVRAM below is another way of referring to the CMOS chip:
Error: Hardware Monitor found an error in [name of component].
Follow this procedure to troubleshoot the error Hardware Monitor found an error in [name of component].
1. Restart the computer.
2. Press the F2 button.
3. In the computers BIOS, check the Hardware Monitor screen for more information.
4. Ensure all internal power connectors are secure.
5. Reset the computers BIOS to the default values.
6. Perform an NVRAM clear.
Given your situation, steps 4, 5, and 6 are your only options since it's not responding to the keyboard. Steps 4, 5, and 6 are essentially everything that was covered above in the directions on how to clear the CMOS, but while you're at it, make sure everything on your motherboard is reseated (Memory, PCI cards, power connectors, fan connectors, hard drive cables and Optical cables, power to hard drives and opticals, etc., etc.
Also, make sure your keyboard and mouse are connected properly. If it's a USB keyboard, you might want to hook it up with a USB/PS/2 adapter and connect it to the PS/2 port on the back of the pc to make sure the keyboard will work. If you have a USB keyboard, you should have received a PS/2 adapter with the keyboard. It's most likely green, with a USB side and a PS/2 connector on the other side. What might be happening is that USB support might not be activated when your pc is booted up with the error you're getting. Connecting it to the PS/2 port instead might alleviate that problem while you're troubleshooting.
