The safeties are keeping the unit from starting for some reason. Some furnaces (at least some newer ones) have visible led lights that may flash signaling a code like (2 fast flashes then a pause and another two flashes, or a steady flash) Look for something like this and check the inner panel for what the codes mean. There may be a small window in the cover panel that will show this light or you may need to remove the cover for the controls area. This may help.
If your unit does not have this set up you may need to call a tech to trouble shoot the problem. Air proving safety switch, loose wire, it could be a number if things. Caution when playing with power. If you are not sure or do not have or know how to use a meter then best to call a tech.