PCI bus failure

Getting "Press to Resume" on boot up. Once is pressed system finishes the boot up normally and all seems to function OK. Shutdown is smooth; no problems. Checked diagnostic lights A, B, C, D on boot up and when the screen has "Press to Resume" the lights are A - yellow, B - green, C - yellow & D - yellow. According to Dell's diagnostic codes this means a PCI bus failure and to remove all cards, re-insall the cards (I assume) and see what happens. No conflicts exists as indicated under device manager.

Can anyone enlighten me as explanation of problem and possible solutions..........please. I get tired of pressing everytime the system it booted up!!

HELP....................HELP...................HELP.....................HELP !!!!

4100, PIII, 1 GHz, 512 RAM, 40 GB HD, CD-R/RW, DVD reader.

Many Thanks,
RWDawg