keyboard not working

First, you cannot connect a keyboard to a serial port. Neither the keyboard or the serial port are designed to communicate with each other.

Next, try booting from a DOS boot floppy.
Does the keyboard now function?

If not, then it is likely that the PS/2 port on the motherboard is damaged.
This usually happens when keyboards or mice are plugged and unplugged with power on.

If you are running Windows 98 or newer, a USB keyboard should work if the BIOS on the motherboard supports it.

If the keyboard functions under DOS, then you have missing or corrupt Windows files.

Check device manager for any yellow "?" or "!" marks next to devices.

For some versions of Windows, you can run System File Checker to look for and replace missing Windows files.

For others, you need to use the Recovery Console, or re-install Windows.

Chas

First of all your operating system is not the cause. The fact that you cannot access the BIOS points away from the OS. At the time you are trying to get to the BIOS the OS has not even loaded yet. Since the lights flash there is no problem with the 5 volt line (pin 4 on the connector) that leaves the clock line and the data line. The ground is also ok or that would affect the 5 volts (no lights)The Clock and Data lines are 1 and two respectfully. You either have an open (broken) condition on one of these lines, between the female plug on the Motherboard or a defective microcontroller chip on the Motherboard itself. A check with a USB keyboard will eliminate the former condition. If it still does not work then its on to the Microcontroller itself. Either way you may not want to persue this much further since it will start to get very technical at that point. I advise that you check carefully the female plug for damaged connections inside and out. After that you may try resetting the BIOS (hail mary there!) but you may have to replace the motherboard or have it fixed by a competent tech, not likely worth it unless it is the control chip and it is socketed. Older PC have a socketed chip. Do not purchase a USB yet, can you borrow one as a test? Oh yes never plug a PS2 keyboard in to a powered PC, you can blow the port because of the current surge created. Older motherboards had a surface-mounted fuse protecting the keyboard and mouse ports. When this fuse blew, the motherboard was useless to the consumer, and non-fixable to the average technician. Most newer motherboards use auto-reset "Poly" fuses that go a long way to remedy this problem. Since you have lights this is not your problem.

yes, usb keyboard is what i would try. if. you have newer os, newer than 98. if you have 98 or lower, is if. if you have working usb device now on that box, , pim, camera, printer, scanner...well ok. no sweat. you know usb is workign. if not, you might have large pain in rear getting usb working. i am just saying.
if it is boss'es computer, maybe 'upgrade' her to sexy wireless keyboard...