will not boot after changing out memory

i made a mistake yesterday when i went to change out the memory from 3gb to 4gb. i had the computer in sleep mode when i unhooked the battery. i did not think that this would be a problem. i installed the new memory out of an existing same machine that was working and when i went to turn it back on all i get is the power light in the front and can hear the cd rom drive trying to work, no video no sounds, nada!! i then took the new memory out and installed the old memory back in it to no avail. if i hold the power button down for 10 seconds i will get a flashing grey light in the front. i am at my wit's end on this one, can anybody help, i have tried the pram suggestion several times and this does'nt work.