PC Won’t Boot

Compaq Pressario 7470 running windows 98,32MB Ram, 6 Gig HD. Someone brought this pc to me saying it wouldn’t boot up. I have cheked the pwr supply, it okay and have removed all of the devices and added 1 at a time (including memory) each cable, modem, NIC card and still get nothing from CMOS. I never hear a beep or anything, I have tried a different video card and get the same results. The fan on the CPU comes on and I hear the HD pwr up, but still nothing from the PC. Anyone have any ideas, Iwould greatly appreciate it…. Thanks…rfm