What am I doing wrong?

I am trying to fire up this W7 PC to eventually use on a PS/2 KVM. The
PC has only one PS/2 connection (plus a few USBs of course). I want
to use a keyboard and a mouse which both are PS/2. I tried using both
the keyboard and mouse one at a time and both work during bootup. So
they both seem to work. Even in W7 altho still only one at a time.
I have to make things work with both mouse and keyboard connect of
course. I then tried using both connected to a Y connector which
changes the connections to the single PC USB input connection. Both
mouse and keyboard still work during boot. However, when I get to W7,
neither work. Funny, since both work when alone. Even when using the
Y connector. So the mouse, keyboard, Y connector, and PC USB port all
seem to be good individually, but not together, which I seem to need.

aarrrggghhhhh!

???

I hope someone can tell me what to try.
Al