Yes, the CD is useful, it is actually a pair of discs for a 126 chassis. It contains everything from the owners manual to wiring diagrams.
The problem is with the pre-glow starting system, more than likely 1 or more glowplug is burned out.
The glow plug relay is in the left front fender well, roughly behind the left headlight. Pull the cover off and see if the strip-fuse is OK. If it is, pull the connector off that has the wires running toward the engine. Using a heavy duty ammeter (0 to 60 amps), plug the ammeter lead into the 5 sockets one at a time and observe the readings. The amp draw should stabilize at about 15 amps after 10 seconds, it will start out higher, then drop after a few seconds. The small numbers on the face of the connector indicate the cylnder number that the socket feeds power to. If you find one or more bad glow plug, you may want to consider replacing them all. If you don't have a means to test the plugs but want to try something on your own, bad glowplugs are pretty common, you could try them first.