When a pc boots, it generally displays on the screen, which key or keys (possibly the Pause or F1 key) you have to press in order to enter the bios.
enter evesham bios
throws up a number of hits.
I suspect when you changed the cmos battery, the pc 'lost' the settings for the hard disc, such that it cannot now 'see' it in order to boot from it.
Re-input the hdd paramters and hopefully it will boot.
Good Luck - Keep us posted.