Why can't my computer can't detect my external hard drive?

My dvd/cd rw drive cant working properly and when i insert pan drive it cant show pan drive in 'my computer' ?

• Respected sir/Madam, Two days ago my DVD/CD-RW drive was working proparly but today onwards when i insert disk it hangs up the computer when i removed disk and tried to open DVD/CD RW drive in my computer it also hang my computer and when i inserted pan drive there is no any link about pan drive in"my computer" i am trying from morning but still not got any result.Hope you can help me.

• Answer:

  try doing a "system restore" in your administrative tools! in the start menu! Also when your computer starts check for IRQ conflicts where the cd asks for assistance from the CPU! if they have the same numbers you may be conflicting the two devices! like multimedia device IRQ 4 Multimedia device IRQ 4 this is a conflict and need to be changed in the BIOS! Also look under event viewer in control panel and administrative tools looking inside at "system" wil probably give you an error ID which you can send to microsoft!