I had a new disk drive installed they left the old one so i could get my info off. my comp. booted fine until yesterday it went BACK to booting with my old hard drive. I called the tech and they said they could take the old one out and it would be fine. I removed it and my comp. booted fine. I shut it down so i could put the sides back on and when I turned it on it went into boot failure. I TOOK the sides back off and made sure I didn't knock anything loose and turned it back on. it kept going into boot failure. I tried this quite a few times. Then I tried turning it on again and it came on. now I'm SCARED to shut it down. I'm afraid when I try to turn it on again it will say boot failure again. what should I do?Sounds as if they may have forgot to set the jumpers correctly and or cabled it wrong.
The new drive if that's what you want to boot to should be jumpered as master and hooked up at the end connecter of the IDE ribbon cable.
The old drive should be jumpered as slave and connected to the middle connector of the IDE ribbon cable.
Below is an ILLUSTRATION of jumpers and where they are LOCATED. It is NOT however the settings for your drives as they are all different. You will need to look on the drives themselves for the individual settings for each drive...



If this does not work satisfactorily your CMOS battery which is located on the MBoard may be weak/failing...replace it
It's about the size of a dime and the part # is CR 2032 available anywhere...

As always when working inside the case remove all power sources and take anti-static precautions.