In-line booster extender for cat5 cable -vga -usb

I HAVE A WIRELESS "N" LINKSYS ROUTER AT THE HIGHEST POINT ON THE 2ND FLOOR OF MY RESIDENCE. TROUBLE IS, THE SIGNAL OFTEN DROPS OUT ON THE OPPOSITE SIDE OF THE HOUSE IN THE BASEMENT OFFICE WHERE MY DESKTOP IS LOCATED. IT IS HUGELY UNDESIRABLE TO RELOCATE EITHER, SO INSTEAD I RAN CAT5 FROM THE ROUTER TO THE COMPUTER. IT IS NOT A STRAIGHT RUN, BUT IS BROKEN UP 3 TIMES ALONG THE WAY. I'VE HAD TO WIRE UP 3 SEPARATE JUNCTION OR TERMINAL POINTS ALONG THE WAY WITH 3 INSERTS AND CORRESPONDING TERMINAL PLUGS. I DIDN'T ANTICIPATE ANY LOSS OF SIGNAL WITH THIS APPROXIMATELY 80 FT RUN. I CHECKED AND RECHECKED THE WIRING OF EACH JUNCTION POINT FOR PROBLEMS. ALL IS FINE IN THERE. I'M GUESSING NOW THE PHYSICS OF IT, CONCERNING BOTH THE LENGTH OF RUN AND THE EXTRA CONNECTIONS DOESN'T MAKE FOR A HEALTHY SIGNAL. I WAS COMPARING IT TO WIRING TELEPHONES WHERE I HADN'T EXPERIENCED ANY PROBLEMS IN LONGER RUNS.

MY QUESTION NOW IS: IS THERE SOME WAY OF BOOSTING OR AMPLIFYING THE ETHERNET SIGNAL?
ALSO: MY MAC COMPUTER HAS AN INTERNAL WIRELESS PORT. IS THERE A RELIABLE WAY (A DEVICE THAT CAN BE PURCHASED) TO
ENHANCE ITS ABILITY TO PICK UP THE LINKSYS' WIRELESS "N" SIGNAL?