Well from my experience in situations like this... it may be the following problems...
When touching a piece of hardware you are not going to feel the heat that the sensors detect in your computer, as chip sensors are for internal heat not external.
If you are receiving temps like this as soon as you boot your pc, then there is a problem with your hardware/software.
Make sure that all of your drivers are up to date, sometimes old or faulty drivers for any piece of hardware can put out faulty readings.
Another issue could be that some of your hardware is failing... but I am willing to bet its the sensors on your computer and if that is the case, you can't exactly fix it other than to replace the whole piece of hardware.
I'm pretty much willing to bet thats the problem, because at 70*C you should be frying eggs on that thing... and if the temp was really 70*C you should be receiving a BSOD or RSOD
Either way, I would attach an external temp gauge to monitor the heat leaving the case, after a while it would put off some intense heat, Other than that I wouldn't worry about unless your 100% sure that the readings are accurate.