zjwo 0 Newbie Poster

Hi,
I recently inherited a dell optiplex gx1. I upgraded the ram, and made some other minor adjustments, but now when I try to boot the system, It tells me "Alert! Cover was previously removed" and after that "invalid configuration information - please run SETUP program" No matter how I try, I can not get this to go into bios or boot the o.s. I've tried all kinds of key combos like CTRL-ALT-DEL CTRL-INS CTRL-ESC... but all to no avail. Any suggestions?