Computer freezes, no errors, just everything dysfunctional

My Sony Vaio laptop will freeze with the following symptoms: After a few minutes (usually from 2 to 60 minutes of working), the whole screen freezes. Mouse or keyboard won't work. There is no activity on the HDD usage light on the laptop. The fan will constantly work at a definitive level (not speeding up or down) The only way to make the computer work will be to hold down the power button and then start it up once again. What can cause such a problem? I can't revert to the last update because the 10 days have passed and I can't just reset the PC because there is so much on my laptop. Thanks

Question by Siamak Ensafi on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.