Dell Studio XPS 9100 Desktop - Peripheral Missing?

Hello,

At startup, some removable devices disappear:

Devices with Removable storage media including CD / DVd, BlueRay / DVd and Compact Flash card reader .... disappear?

I really do not know why because this is a morning at the opening and disappears shortly after,

if I made a reboot I  only have the CD / DVD player and the others are gone.

Where is the problem?

Can we please help me with this problem, where is the solution?

Thank you in advance

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System Information:

Dell Studio XPS 9100 - Windows 7 Intégrale Édition (64 bits) Service pack 1 - BIOS Version A04 - Intel Core i7 - Firefox 38.0.5 - McAfee Security Center