<< if your hardware is 10/100 it's probably you cables
sometimes a damaged or improper cable will work at 10 but not 100 >>
Yes, I had this bug. My cat5 cables were 1-1. pins 1-8 went to pins 1-8 on the other end. This will work in 10mb but will NOT at 100mb.
The reason is that the twisted pairs need to be used...so 1 and 2 need to be on same twisted pair and 3 and 6 are the other. If not, there is too much noise, as 3 and 4 would be on the pair not 3 and 6.
Hope this makes sense!! In this case, the "bad" cable will STILL look OK
with a meter, but they must be physically on the twisted pairs to work. Also, if this cable is bad, you can still ping on the 100mb net, but can not transfer files!