I was having this issue not long ago. Come to find out that the new power supply I purchased was defective. Where it sent power to the fans, but the computer just wouldn't fully turn on. Worked fine with my old power supply. Did the same when I put the new power supply in other computers as well.
thx for your reply much appreciated i forgot to mention that it finally boots in after a while and then doesnt miss a beat when its going.looked further into it and i disconnected the scanner no problems since maybe as you said too much for PSU thx again