I completely agree with KattyKit about getting rid of Norton.
However to deal with the short term problem,this is what Norton say -
STEP 1: Delete temporary files Run a tool to remove temporary files.
(CCleaner would do) Restart the computer.
If the problem persists, continue to
STEP 2: Turn off floppy drive scanning on shutdown
1 Start Norton AntiVirus.
(If Norton AntiVirus is installed as a part of Norton SystemWorks or Norton Internet Security, then start that program.)
2 Click Options.
3. If you see a menu, click Norton AntiVirus.
4 In the Norton AntiVirus Options dialog box, in the left pane, double-click Auto-Protect.
5 Click Advanced.
6 In the right pane, uncheck Scan floppy disk in A: for boot viruses when shutting down.
7 Click OK.
8 Restart the computer.
From
HERE