The color cable one needs in high speed internet these days is BLUE.  Blue ethernet cable is the usual standard for 1000 megaHz cable.  Twenty dollars should buy a BLUE replacement cable with no difficulty for most individuals.  How could you tell if you have a bad ethernet cable without test equipment and a technician??  Take the cable at the computer rear panel and insert that end into the satelite transceiver. Take the transceiver end and place into rear panel.   How has the situation changed, because of the swap?  Was download slow and now upload is slightly slower, was upload slow and download is drastically slower.  The internet does something else now.  For any change, excluding no change, you have a bad cable.  New and bad cables surface 24/7, even if the installer installed them.  If they don't have a blue cable a red one may(?) suffice.  The lowest option is the overgrown looking cable that looks similar to the cable leading from the telephone to the wall.

Unscrupulous computer techs do exist.  They may sell on rare occasion, used equipment as new.  Your ethernet card should be rated 10/100 MHz or 10/100/1000 MHz...seen 1000 MHz spoken of before?  A cable should match the highest rated capabilities of what it is connected to.  And also, in the case of poor or older product, the card could be rated lower.  !Beware cannibalized parts!  Twenty dollars should get you a brand new top notch ethernet card.  Should you think that the problem may be this issue.  You can find out about your ethernet card in network connections and properties in the control panel.

Now that you are back there at the rear panel, is your card in the slot well enough to transfer good signal?

If you have a chipset ethernet you can use troubleshoot in systems in the control panel to determine if you chipset is working properly.

And lastly, just as on you new telephones the little wires that make the connection inside the sockets the ethernet cables go into can become bent or a myriad of other problems with them.  Get your reading glasses, a flashlight and inspect them.  You need to be careful straightening them, they are not difficult to break.

Try checking that before going berserk over lack of speed.

Itpropender

for some reason i had this flashback to the scene in "the abyss" where the guy has a green lightstick and is told to cut the light green, not the white cable...

but seriously. don't go judging a book by its cover, or a cable by the color of its mantle. if you want to spend twenty bucks on a blue cable, well, i can get me some for a few bucks a pop. they might even carry a signal. sometimes. and if you have more extra cash lying around, there's some prime florida swampland going cheap, and i hear the area is going to be developed reaaaaal soon...

th op gave some sound advice in recommending to use good quality cabling. but go by what is printed on the cable or the box it came in, not by the color of it. (you can order cables in pretty much any color you want)

and expensive is not always better. take monster brand hdmi cables. the will set you back hundreds of dollars and give no improvement over bottom of the bin cheapo brand cabling. (as long as that cabling is standardized to the hdmi specs., this is where labeling of the cable comes in. it might look cheap, feel cheap, taste cheap, but if it is specced right it will do just as well as the expensive stuff.)

Also, call your ISP before straightening any of their wire contacts, they may want to do a swap out.

btw, there is a certain time after submitting a post that you can go back and edit it using the modify button. although i am not sure what ca3le has that set at right now...

 In the field I'm in, the blue cables are made for plenums, which means they are rated for use in HVAC ductwork. Mainly for identification, I have also seen it red, and the standard grey. Makes no difference as rosop said, just look at the rating.