computer all funky after reformatting drive

I reformatted my hard drive a few days ago. It was partitioned in two, but I erased the partition and reinstalled osx 10.4.11. Now my internet acts all funky, firefox won't catch on often so i have to quit and restart a bunch of times for the page to load. the computer in general also just acts slower and weirder. i just imported 70 gigs of music from a friends pc western digital hard drive. im thinking that may be part of the problem, buti dowloaded the virusbarrier trial and it didnt find anything though. any suggestions? thanks

Will not be a virus unless it came with the music.

Partitions were removed when you reformatted the drive and Disk Utility Repair Disk reports all okay? How big is the HDD as you need about 20% free to enable the drive to work at its optimum.