Bios not detecting hard drive -- intermittent

Suddenly, without any apparent reason, neither of my 2 hard drives are detected during boot, sometimes.  Meaning... they weren't detected using auto detect.  I changed BIOS settings to USR and put in the numbers, still not detected.  Switched back to auto detect.  I figured it might be the cable, so I put in a brand new one.  On first boot, they were detected, everything was fine.  Yippee, problem solved.  Nope.  Rebooted, again not detected.  Jiggled things around, they were detected.  Plugged in my other drives (CD, floppy) and they (the hard drives) weren't detected.  Unplugged the other drives, still not detected.  Removed/replaced the hard drive connector, they were detected.  I don't see any bent pins.   I don't know if my jiggling/replacing had any real effect -- might have just been coincidence, since sometimes that method was not effective.  Right now I am using this system while it detected the drives, so the drives are fine.  I've had these 2 drives working for at least 6 months and haven't made any changes inside the chassis recently.

If it isn't the cable or the connector, and it isn't the drives or the BIOS, what could it be?
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CallandorConnect With a Mentor Commented:
If the system froze up when you tilted it, you have something loose or shorting.  Follow RID's advice and check connections and cables.  This may be the source of your problems, and not the CMOS battery.
Could be where the cables hook to the motherboard and that connector on the board could have a problem
Two possibilities: your CMOS battery is failing, or your IDE devices are causing interference.  Try each one separately, on the other IDE channel, and in another machine.
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options to reduce the possibilities.

A. if the hd these are using the primary ide slot , consider putting on the secondary , and doing
reboots to see if the drives continully get noticed in auto detection , if they work perfectly in
this scenario  consider adding 1 of the cd-rom drives to the primary controller and see
if gets atuotdetected , if it keeps appearing every once in a while , your primary ide
slot has failures.

1. insert a new or used hd in that tower that has never "ever" been plugged into it ,and see if the
same problems occur , if they do , then it could be power/motherboard issues. since you already
rulled out bentpins/bios configs,cables and etc.

2. insert the drives that are in that case on to another computer and see if the problems
are not being caused by the drives itself.

3. is the ribbon your using ata100 or udma66. problems like mentioned can be caused
by a incompatible ribbon cable.

4. open the case and leave 1 panel off, check to see  when the hd's are being detected
if the motor in the hd is actually performing by  looking for sounds or motion in the hd.
dont touch any of the underlying electronicsof the hds while on.

5. if the drives are farelly newer than the board , and the hd's were replacments .
they may have problems with older boards , bios upgrade would help this scenario.

6.running a manufacture diagnostic tool on the hds , can help you determine if any errors
occur durring the tests , if so the hds can be the problem

7. in testing hd issues its best to only use 1 drive in the tower.

9. molex power issues ,  consider using another molex on the drives that is being used by another
or free molex for the hd drive . a bad molex can have bad effects on startups.

these are the options that id consider taking , at the moment i cant remember of anymore,
but either way in your situation its all a matter of troubleshooting consider starting from
#1,  and crossing the checklist. it sounds like your very competent on what your doing
so id think you will be able to find the cause very soon
to slow :] "sorry if repeat"
robin286Author Commented:
To rule out failing cmos battery -- I'm not getting any specific messages that indicate this.  Is there a test I can run that will show me how the battery is doing?
Either temporarily take one from another board or buy a new one - they don't cost that much.
robin286Author Commented:
I tilted my case to look at the battery, system froze up, had to reboot, hard drives not detected.  I removed the connector and replaced it, and then they were detected.  I neglected to mention that the system freezing up was what happened to me in the first place yesterday, forcing the reboot in which the HDs weren't detected. I'm running XP and haven't added anything new lately.  I run antivirus and spyware checks daily and keep those current.  Don't know if that info is relevant, but I thought I'd include it just in case.

So, I will replace CMOS battery and see if that helps.  I have a lot of cables laying around.  How can I visually tell the difference between ATA and UDMA?  (The cable I am using now has the blue connecting into the MB, with a black connector to the master and gray to the slave, with the red stripe along pin 1.)

If it is the connector (molex?) itself -- how can I replace that? It doesn't look like a removable part on the MB.  I have a MSI 845E Max (MS-6566e ATX Mainboard).

When BIOS does detect the drives, everything appears fine.  And like I said, it's been doing fine for months -- this just happened out of the blue.  Which leads me to believe that something has now gone bad or is going bad.  
ridConnect With a Mentor Commented:
System freezing when you tilt it?
Sounds like a bad connection somewhere, not necessarily to do with the hard drives. Check all components for proper seating (CPU/heatsink, RAM modules, etc) and make sure there are no loose screws or similar that may be doing intermittent mischief as you reseat connectors and such. Also, power connectors should be checked and all cabling to floppy drive too.
if necessary, remove everything from the case, inspect all connectors and fixings, and rebuild it from scratch.

robin286Author Commented:
I pushed around on all connections, a couple of them felt slightly loose but I didn't have any "eureka" moments.  However, I was able to plug in all drives and have the darn thing boot properly several times, so that must have been it.  Thanks for all the help, guys!!
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