RJ45 is a standard type of connectors / plugs for network cables.
Such connector / plug terminates flat stranded cable, such as Cat5 8X8, in data applications. RJ45 has eight pins to which the eight wire strands of a cable are connected electrically inside of the RJ45 plug. Notation "Cat5 8X8" means that the ethernet cable is of the type "Category 5" with 8 wire strands at each end (8 narrow wires inside of the common enclosure ("jacket") of a network cable).
Without a plug it would be impossible to connect an ethernet cable into a computer port, and RJ45 seems to be one of the the most wide-spread type of plugs.
If the connection between the ethernet cable, such as Cat5 8X8, and the computer becomes flaky, then it is necessary either to replace the whole cable, or to cut off the old RJ45 plug together with a short piece of ethernet cable, and to install a new RJ45 plug.
Below is a short algorithm how to attach a new RJ45 plug to the Cat5 8X8 cable.
* Cut the outer jacket of the whole ethernet Cat5 cable about 1.5" to 2" from the end. This will give you room to work with the wire pairs. Separate the pairs (8 wire strands are organized into 4 pairs) and separate all the wires in all the pairs to approximately 1/2" in order to have some length of "untwisted" wire near the connection.
* Align the eight separate wires in the definite order which is described below (and also depicted on the attached photo, click on the image to enlarge it). It is extremely important not to make a mistake and not to alter the the order of the eight wire strands. The order described below is officially known as 'EIA/TIA 568B wiring standard', and this particular wiring standard is used in the ethernet Cat5 cable that links 'WeatherLink' and processor 'c1pem1' (see 'Weather Station' wiki40 page). It might be that some other network cables in our lab have different order of colors of wire strands, because there also exists another wiring standard 'EIA/TIA 568A'.
1 - Brown w/White Stripe;
2 - White w/Brown Stripe;
3 - Green w/White Stripe;
4 - White w/Blue Stripe;
5 - Blue w/White Stripe;
6 - White w/Green Stripe;
7 - Orange w/White Stripe;
8 - White w/Orange Stripe.
Reminder: this is true for 'EIA/TIA 568B wiring standard' only.
* Insert the wires into the connector making sure that each wire goes into its appropriate "channel" and extends all the way to the end of the the connector underneath the gold crimping connectors. If the wires don't extend to the end of the connector, the crimp may not make contact.
* Press the cable and the jacket into the connector firmly so that in the ideal case the jacket will be crimped by the plastic wedge near the rear of the connector (this is not so easy to fulfill, because you needed to cut and take off exactly the correct amount of the jacket at the very first your step, otherwise you will have the situation that there is some area of the Cat5 cable between the RJ45 plug and the beginning of the jacket where 8 fragile wire strands are not covered by the jacket. Although if you do not expect to bend your Cat5 cable near the RJ45 connector, this situation of bare wire strands is not too bad).
* Insert the RJ45-connector with 8 wire strands touching the inside pins into the special crimping tool (you need to make sure before you start the whole procedure that you have this tool) and crimp the RJ45-connector with the Cat5 cable in it.
* For double safety, in order to be absolutely sure that all connections are made inside of the RJ45 connector, you might re-crimp the cable, that is to repeat the previous step.