XP PRO PC running very slow

I’m running xp pro/sp1 on a Gateway Demension 8100, 1.3 gighz with 256 of ram. My pc apps are running excruiatingly slow. I removed all programs from the start memu, including the registry. Some improvement, but far slower than the hw specs would suggest. I’ve checked for viruses using a boot disk, I running checkdisk, defraged, all to no avail. Any suggestions!!????