Need a little help

[ichabod crane]

i have just recently re built my pc after cleaning my water system out and buying a new PSU, but i have a little problem, when ever i turn the PC off it wont turn back on again with me reseting the CMOS. it reboots ok its just when i switch it off, also there is no bios warning about the cmos battery being dead or low. any help at all will be much appreciated thanks