Dewalt 3/8" Drill Acting Up

I have a Dewalt 3/8" corded drill. It has been used some lightly for a few years.Good drill no where near worn out. It has really been lightly used....maybe 4 yrs old at most.
Anyhow today it wouldnt start at times..I blew it out with air compressor and it seems to help. What is going with it? It will work a bit and not work some!

check your variable speed trigger control knob. either that or the brushes. you could remove the brushes and then put them back in. should work.