I have a dewalt dc618 finish nailer When I go to shoot the lights on the gun start to flash and will not shoot ?

https://www.weeklytools.com/dewalt-angle-grinder-buying-guide/
When it comes to Angle Grinder, the name of the Dewalt tools maker comes first. We will look at the basic parts and functions of a grinder before purchasing a machine. Then let's see the details without delay.

Its all about power. If you have air pressure and its the right nail it will shoot. If its oak or maple nope it most likely cant drive it up. If your pressure switch has a 90-120 spread, it will work at 120 and fail at 90. You sometimes can good results by bumping it up 5# or so without the pop off loosing its cool.

firstly its always better to change both of the bands even if one is broken this always keeps the drive trim.all seems well clean all the contacts ie battery and gun (do not use any cleaning products this will cause grease)just wipe clean with paper towel.

The link below is where you can download the owners manual. The link is on that page near the top right hand side under the area marked downloads. Page 5 will show you were the switch is located that switches the tool from sequential fire to bump fire.

DeWalt DC618 parts and operations manuals

Parts and parts diagram available at www.toolpartsdirect.com
I use this company quite a bit for parts. Good luck.

I know a lot of Dewalt nailers will not shoot properly once the battery is starting to get a little worn/has a lot of charging cycles on it. Their picky about having fresh batterys. How old is the nailer/batterys?

Check the battey then take it out and check the driving rod. On the front of the gun, flip the latch and make sure it is pushed all the way back.
make sure you have nail, of course. put the battery back in. If al that does not work, have it services at a dewalt service center.

just goto:
http://www.retrevo.com/search/v2/jsp/mytrevo/myTrevo.jsp?page=man

download the support manual. You should be on your way

problem solved.whoever had used the tool must have hit something hard because the drive pin had been pushed back just enough to stop it from cycling.

I have both the DC616 and 618 and have used them sucessfully for about three years. Two main things go wrong. There is a drive belt that breaks (drives the spool that give the energy to drive in the nails), second are two small rubber bands on either side of the drive head that break. The bands can be accessed by taking off the front silver cover, the drive belt is access by spliting the case. Make sure you are using the correct nails or the drive pin may become bent and will jamb repeatedly. Hope that helps!