|If you have not tried more than one data cable, most likely you have a data cable problem.|
This is about IDE cables but the same applies to floppy data cables.
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.
" I guess when batt in DS1287 chip is dead..."
I have a old mboard circa 1995 (Gigabyte 586AT) that had that problem, but it had no effect on whether the floppy drive was detected properly. It just couldn't retain the time and date, or other custom bios Setup settings.
I found out that it's RTC, ODIN OEC12C887, is no longer made, but can be replaced with a Dallas DS12C887, or a DS12887, which has a Y2K problem. Dallas (Maxim actually - bought them out) says the original Award 4.51PG bios will probably not work with the DS12C887, so I obtained two DS12887 RTCs, installed one in the mboard, the other other one is still sitting around. The lithium battery inside the modules is only expected to last 5 years, and they are at least that old, however, they usually last longer than that. The mboard was recently fried by a failing power supply.