|What brand name and model of computer do you have, or if you have a generic system, what is the make and model of your mboard?|
Has this computer worked properly previously?
"bios setting have been changed"
"when i replace.....the cmos battery"
Some bioses will display such a message if the cmos battery has been removed and then replaced, or if you clear the cmos by moving a jumper then moving it back, or if you press a key at the wrong time while booting if the cpu has been set up by the bios rather than jumper settings on the mboard, or if you have changed the cpu, or if you have changed the amount of ram you have installed, or if you have changed which drives you have installed, or if one or more drives that were detected before are not being detected.
If you also cleared the cmos by moving a jumper, did you remember to move it back to the normal position?
You must set at least the time and date in the bios to other than defaults, or set them in Windows which also does that, after the cmos battery has been removed and then replaced, or if you cleared the cmos by moving a jumper then moving it back.
Assumimg you made no changes to the connections of your data cables to the drives or the cable select or master/slave jumpers on the drives and they're connected correctly, and the cables are not damaged, and you remembered to plug in their power connectors, you may need to go into the bios and change the default settings it has been set to because the cmos battery has been removed and then replaced.
Your bios must see the drives as well as your operating system - if they don't show up there, you did not connect something right, or one or more data cables are damaged, or the bios is set to not detect a drive connected to a connection they are connected to. If an operating syystem is not found, if you have a hard drive with Windows on it that booted before, you may also need to change boot order settings or other settings in the bios if you have more than one hard drive and one is not bootable.
"the newly installed dvd drive"
If that drive is IDE, and a DVD combo drive (reads and burns both CDs and DVDs) capable of 16X or greater DVD -R or DVD +R speeds, it MUST be connected to an 80 wire data cable in order to work properly at it's higher speeds.
Other than having more wires, 80 wire IDE data cables have a blue connector on one end - that end MUST plug into the mboard.
New IDE drives usually come jumpered either cable select (CS) or master (MA).
If you installed it on the same data cable as an IDE hard drive or another IDE CD or DVD drive, both drives must be jumpered cable select, or one must be jumpered master, the other slave - you do not mix the two types of jumpering. If both drives are jumpered master or slave, neither one will be recognized by the bios or the operating system. If the other drive is master, some brands/models of hard drives (e.g. Western Digital) have two ways master can be jumpered - one way for when it's by itself on the cable (Master, single, or similar), the other way for when another drive is jumpered slave on the same cable (Master, with slave present, or similar).
If an IDE drive is by itself on a data cable, if it is jumpered cable select it should be on the END connector of a 3 connector cable; OR it can be jumpered master and be on either drive connector on a 3 connector cable; it may NOT be recognized by the bios at all if it is jumpered cable select and on the MIDDLE connector of a 3 connector cable, of if it is jumpered slave on any connector (and by itself on the cable).
It is common to un-intentionally damage IDE data cables, especially while removing them - the 80 wire ones are more likely to be damaged. What usually happens is the cable is ripped at either edge and the wires there are either damaged or severed, often right at a connector or under it's cable clamp there, where it's hard to see - if a wire is severed but it's ends are touching, the connection is intermittant, rather than being reliable.
Another common thing is for the data cable to be separated from the connector contacts a bit after you have removed a cable - there should be no gap between the data cable and the connector - if there is press the cable against the connector to eliminate the gap.
80 wire data cables are also easily damaged at either edge if the cable is sharply creased at a fold in the cable.
Try another data cable if in doubt.
If any drive is SATA...
Check your SATA data cables. The connector on each end should "latch" into the socket on the drive and on the mboard, or on the drive controller card - it should not move when you merely brush your hand against it near the socket - if it does, use another SATA data cable that does "latch", or tape the connector in place.
(There is a slight projection or bump on one side of the outside of the connector that "latches" it into the socket - it's easily broken off or damaged)