Life or use expectancy of an Inspiron 17R

I have an Inspiron 17R laptop. I purchased it August 2013. What is the normal life expectancy of the computer laptop? Particularly the mother board. I am faced with this problem as of October of this year. I have not had for at least 3 years. I thought I would purchase another laptop because of it being outdated not the mother board going. I have sought repairs and have been quoted 300 to start on up to more than 500. If I have to buy another computer this makes me reluctant to purchase a dell again. I truly loved my computer when it was working, then one day I cut it on and it does not power up. I was always careful and kept my co outer cool.