Window update or software problem

By continue to the window, I'm assuming that this powers on, but won't go past a black screen.

You did say it hasn't been used in a long time, so I'm also assuming that it's been a LONG time.

Before you try anything else, get a new backup battery into this. (coin cell, CR2320) It's on the mainboard, and should be easily visible.

After that, and setting the time, (if you get to the BIOS screen (F2)), it may still take a couple of tries to get this to actually boot fully. (assuming it's still functional)

Old boards can get pretty funky about starting after a LONG period of non-use, but it should boot after a few tries, with the power cord in and live.

When you open the case to check the battery, look at the mainboard for bulging or leaky capacitors (the round small cans on the board)

If you see any, (which will probably the row of caps closest to the CPU cooler), the board is probably not functional, and, even if it does start, will not be really useable.

(They CAN be replaced, but how badly do you want to use this 20+ old year computer?)