that does indeed make it worse.
removing the battery will reset the bios - windows accesses (and can change options) the bios - so it could be either
when you say won't boot ... how far does it get?
press the button .... and then ... what?
do the fans kick in?
does the network card ... or any other leds light up
check all the connectors are OK - it's possible that by removing the battery you are actually flexing or disturbing something else. (worst case - the mobo has a bad track)
try booting from a 98 floppy (floppy will happen "naturally" so I'd try that first -
http://www.bootdisk.com/) or cd (knoppix, ubuntu or ultimate boot cd or) when it won't boot normally.... it's possible that it's the O/s - a boot disk will eliminate the hard disk.
two things I'd also do is update the bios firmware
and then the mobo chipset drivers (might as well do all the others if you can as well)