IBM R40 LAPTOP NOT WORKING

Take to repair store.

It's quite possible that the battery is finally dead. Batteries don't have an infinite life span for charging. Just because a light comes on doesn't mean it's actually holding the charge.

When you turn the computer on, is it still plugged in or are you trying to boot it up in battery only mode?

It's an IBM so if has to be old. IBM no longer makes personal computers. So exactly how old is it? Sold its manafacturing wing to China. Given the age, it could also be another hardware issue as well.

FWIW, while IBM themselves doesn't make pcs, their Chinese 'partner' does. Lenovo makes pcs and IBM distributes them through their channels in USA. In fact, I'm communicating with one (ThinkCentre desktop) right now. I bought one through a friend's IBM employee benefit discount.

Lenovo acquired the former IBM PC Company Division in 2005 for $1.75 B. Lenovo's executive headquarters are in Research Triangle Park, North Carolina.

"IBM became the owner of 18.9% of Lenovo in 2005 as part of Lenovo's acquisition of the IBM personal computing division. Since then, IBM has steadily lowered its shareholding in Lenovo. In July 2008 the IBM shareholding went below the 5% reporting disclosure threshold."

If the pc doesn't come on, how do you know whether or not there's a problem with the OS?

I'd say the Battery or Power Supply is suspect, just as a guess.