|Is this for all computers or only one?|
If only one, then likely it's a NIC issue specific to that PC. If it's all PC's, then the most likely answer is, you have them all plugged into a 10 Mbps device.
You can, and should, check that all NIC's on all PC's are set to "auto" for speed. It's possible you've got them all manually set to 10 Mbps.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.