2000 chevy blazer 4 wheel drive not working right

So I have a 2000 2 door 5 speed chevy blazer ls, and when I
push the 4 hi button it blinks 4 hi and low then goes back in
too 2wd, but if I push 4 low, it goes in, but both hi and low
lights light up!! How possible is it that the vacuum switch
on top of the transfer case is bad, I took off the lines and it
looked like there was some gear oil in them, so my switch
could be bad and I need a new one, then blow out the lines,
what do you guys think? When I try 4 hi the computer
doesn't even click, I'm a little confused!! Help me out
please!!!