On an old system with the typical flat ribbon cables you may simply need to throw in a fresh one or pair. Thay get hardened up after so long and lose conductivity seeing intermittent or simply no results.
Another thing to look at on any old system is simply the $2-$3 lithium battery on the board itself. Any time after a full year of use those can simply get weak and start seeing the loss of cmos information along with other things.
For new builds here in the last 3-4yrs. the substitution of flat ribbon for Antec's dual nylon covered ide cables allows taking them from one build to the next. The shipping costs equal the retail price for those however!
