Without knowing which OS you're running, I'll assume it's XP. If that's the case, here's a few things for you to check...Start | Run | Type services.msc, and click OK | Scroll down to "Shell Hardware Detection", right click and select "Properties" | Check to make sure the "Startup type" (under the "General" tab) is set to Automatic.
If you're running the Pro version of XP...Start | Run | Type gpedit.msc, and click OK | Expand the following branch in the Group Policy Editor:
Computer Configuration | Administrative Templates | System
Check your settings in the RH pane for "Turn Off AutoPlay", by right clicking and selecting "Properties" (and modify as needed).
Start | Run | Type regedit, and click OK | Expand the following branch...
HKEY_LOCAL_MACHINE | SYSTEM | CurrentControlSet | Services | Cdrom
Check to make sure the AutoRun DWORD Value is 1. If you need to modify the Value, right click the Value name and select "Modify" | In the "Edit DWORD Value" window that opens, enter 1 as a hexadecimal value in the Value data field.