First of all, no one can ever be sure that they don't have any malware. Just because your AV doesn't find any, it doesn't mean that you don't have them. I'm not saying that your problem is caused by malware, but it's something to keep in mind.
You left out one piece of info: What are the source and destination of the file you're copying? Are they both in the same HDD, HDD to HDD, thumb drive to HDD, DVD to HDD, etc.?
Even 14 MB/s is quite slow. My configuration (AMD 7750+ & 4GB) is roughly comparable to yours and I get 40-55 MB/s copying partition-to-partition within the same HDD. Copying to and from thumb drives and CD/DVDs are much slower.
*img69.imageshack.us/img69/430/copyspeed.png
AV progs and file fragmentation can slow things down, but not to the speeds you're getting. Assuming that you're copying within the same HDD, the slow speed could be caused by a bad sector, a corrupt file system, some background task with a high CPU usage. What is your CPU usage when idle and while copying? Are other tasks also running slow?