missing CD when dongle in usb on boot up

Hi

I have a Dell 755 dual core, I loaded win 7 had a problem was with my CD rom, on boot up it was there, in devices it was there name and model, but as soon as I put CD in and opened the CD it would disappear off the machine sometime it would read what was on the disc and then disappear, I asked many question nobody gave me an answer. I installed it on a Dell 270 it works great.

Now on Win 8, the problem I have is if I have my mobile modem in the usb when I boot up my CD rom doesn't appear, if I take the modem out and boot up my CD rom is there with the drive letter G, when I put the modem in the CD remains and works correctly.

Any ideas as to why?

I assume the "Dell 755" is an OptiPlex 755?

When you installed Win 8, did you install the Intel motherboard chipset drivers, from Dell?

Dell only supports XP and Vista on this model, but the Vista drivers will work for Win 7/8.

Product Support for OptiPlex 755 | Dell US

Hi
Thanks for your mail.
Yes I have downloaded the divers from Dell and Intel, update bios to the latest.

it only does it sometimes when I leave pen drive or modem in the usb, boot up next day, having said all that, of late I've not noticed it missing.

I had this problem with Win & on this machine, it would boot up OK with the CD ROM as soon as you put a CD init would read it then disappear of the computer altogether, untill reboot. so i went to Win * instead, i have another Dell GX270 win 7 works well on that no problems what so ever.

Thanks again

When this happens to me , it means that the USB device had been auto-assigned the same drive letter as an existing partition / DVD drive on boot up.

I have sporadic problems with a USB device and my UPS monitor. If I leave the USB device connected and boot up in Windows 7 it will sometimes not recognize the USB attached UPS monitor. This doesn't happen in Windows 8.

As I know what the cause is, I try to remember to disconnect the USB device, The device in my case is the wireless transceiver for my Frontier Tranzport, wireless controller for my recording studio program. The Tranzport has to work in a compatibility mode as its an old device and not supported for newer Windows systems.