I can only say what I would do in this situation, so here goes:
1. Strip out Norton, all Norton and anything Norton
2. Backup the Sonar files to CD, in case there are config files required
3. Make note of Sonar settings I may need to re-instate
4. Un-install Sonar
5. Re-install Sonar to the fastest disk on your computer
6. Defrag all hard drives using stock defrag or diskeeper
If you do want more speed, consider building a RAID array for your audio files, with at least two hard drives, plugged into a PCI RAID card, such as a Promise SATA pci.
The more hard drives you have in the array, the quicker it will be. Four is ideal, but may not fit in your case, and may cause cooling issues. Two SATA drives mirrored will be quicker, though. (2x80Gb, for example, to create one 80Gb drive). Hard drives should have a dedicated 80mm fan, to keep them as cool as possible, especially Western Digital.
After surviving a recent data disaster, I will never trust any of my critical files to:
1. A system partition (or the first partition on a drive)
2. A single hard drive
You said you have a separate drive for your Audio files. Ensure this drive is not on the same ATA channel as an optical drive such as CD ROM or DVD, at the very least.
As mentioned in the previous post, without much more known about your system, we cannot advise you further.