Nothing happens when turn comp on

hello i am so lost.. first off i'm a newbie when it comes to rebuilding comps. and such. but the other day i was going to install a slave hard drive so that i could have another hard drive in this comp. well i disconnected my old hardrive, plugged new one in and reformatted it to be like new... then i was going to put the harddrive into the case and mount it... thats when i hit a prob. the mobo fan was in the way and also the flat lines that connect from the mobo to the hard drive, cd-rom... etc... so i unplugged the cords (after numbering them to remember which one went where) and i started to unscrew the fan. but i changed my mind half way through unscrewing the fan. because i decided maybe i shouldn't mess with things i dont know too much about yet. so i screwed the fan back in the rest of the way and plugged cords in. put case back together and started er up...... no beep no monitor signal!!!!!!! f*ck me!!! any one have any idea what could have happend? also i was using a magnitized tipped screwdriver<<<<<< friend said it wouldnt be strong enough to cause any damage... is he right? any ideas?? please help