LAN Cable troubles

I need to connect 2 laptops together; everything successful when I have them in the same room and I use a cross ethernet cable, each one is able to see the other one and to share internet connection.

Obviously I need them to be in 2 different rooms, and I set up a cable for this purpose. The first 12 meters of it run inside the wall, so I used a shielded ethernet cable. Then we go outside for 15 meters, and I used an unshielded utp cable (4cables made of solid copper). Then, 1 meter more into the wall, shielded cable.

This line is straight, and ends both sides with a Rj connector. Host_A is connected by a straight cable, Host_B uses a cross cable.
As a result, the whole line behaves like a cross cable. I tested it, and all the connections are solid (soldered) and exact: 1-2-3-6 goes to 3-6-1-2. There are no mistakes.

Here's the result, after some minutes of connection:
Host_A sent about 70K packets, and received only 10
Host_B sent and received about 50 packets

Host_A sees Host_B
Host_B doesn't see Host_A

Host_A's network card has orange led on and still, green led blinking quickly and regularly
Host_B's network card has green led on and still, orange led on/off like a hard-disk's one.

Looks like the cable is destroying the signal... Is it possible for a so short (30m) cable?

Many thanks in advance to everyone who will help
Michele from Italy

Your cables should last a lot longer than that, I would try to use just one kind of cable, if you run your cable for only 30 meters of UTP should be fine, unless you are running the cables through a lot of electrical work. How were you connecting the STP and the UTP together anway?

In fact, to avoid any problem related to electrical stuff, I used stp where needed.

I joined stp and utp by soldering each tip, making sure different cables cannot touch and short-circuit things.