Motherboard temparature rises 100°C

Rakib mate unfortunately I am on my laptop right now but try running HW Info http://www.hwinfo.com/download.php < pick thr 32bit version.

See this

Using HW Info PSU

Download HW Info and pick the right bit version - HWiNFO, HWiNFO32/64 -Download -(copy and paste thissite into the search bar) If you do not need the running information in thesmaller right hand panel close it. In the left hand window click on the + forthe individual device groupings and they will open out to the variouscomponents.

Go on opening out further until you get to the device itself. click on it andit will highlight. In the right hand window there will be a very detaileddescription of that device as in brand, speeds model number etc etc These arevery detailed and are just what is needed for searching for drivers etc.

See my pic for an example - in this I have shown my power but it is a laptopand a desktop will show more details if you scroll down that listing.
This is for volts but just see when you run the Sensor if there is a readout for the motherboard temp - frankly I don't know what that program of yours is seeing as motherboard. If it was showing the GPU then I would understand even though that would be too hot.

Now I take it this is quite an old machine so have a look inside and check out the cleanliness inside the case, and if all the fans are working.

personally id say it was just a rogue temperature reading, much like speed fan and my GPU being 143c under no load!!

At those temps id expect there to be some kind of thermal cut off or at least some blue screening.

Try a few other temp monitoring apps and see if theyre different, or jsut to prove if you have a dodgy temp probe.

Here is mine, as you can see the third reading is completely false. You have nothing to worry about.