dvd drive missing

Hey i have this problem:
My build-in dvd drive is missing from “my computer” (i have a Acer lap top)
with XP.
When i turn on the laptop,the Acer screen comes up forced me to go to set up.And every time i must go exit-discarding changes to enter the windows.
I tried to do the registry trick that i saw in some articles
[Start] [Run] [Regedit]
Registry Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\Class
Key Name: {4D36E965-E325-11CE-BFC1-08002BE10318}
Value Data: [Delete All Value Data from UpperFilters and LowerFilters]

but there wasn't any UpperFilters or LowerFilters there.
Any ideas?
Thanks in advance.

Replacing your CMOS battery should help. If you want me to try and find the link on how to do so, post your computer's model number.

EDIT: You also might want to look around in the BIOS for enabling a DVD drive, but then again, I need the model # please.

The model is
Acer TravelMate 251LC_DT
Intel pentium 4 2.5 GHz
1.23 gb RAM

Εdit:
This morning didnt get in set-up page in the first time that i open the laptop but later in the day the set up page come up again.
And also this kind of problem happend a few months earlier but somehow it fixed all by itself.

1. http://aumha.org/downloads/cdgone.zip
or...
2. Go to Device Manager, click a "+" sign next to IDE ATA/ATAPI Controllers.
You'll see two items:
- ATA Channel0 (or Primary Channel)
- ATA Channel1 (or Secondary Channel)
Right click on each of them, and click Uninstal. Confirm.
Restart Windows. They'll be automatically reinstalled.

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