That crimper looks sorta cheap. Using a hand held crimper can sometimes be a bit iffy as its not always reliable so the tester should help. Cables with RJ-45s on them are pneumaticly pressed at the cable manufacture. Look for the pin blades to strike the copper wires at 90 degree angles. If its off, it can easily result in a bad connect.
If your running the cable long and have problems with getting a signal even though the tester says its good, turn off auto negotiate link speed (at the PC) and set it to 10mbs under the the properties tab of the network card.
Good luck.