No power on acceleration

I changed the valve cover gasket and the oil filter and now when I try to drive the car it doesn't have any power.  It starts and idles good (even in nuetral), but once I put it in drive and try to go the dash lights start to blink, brakes do not work and the more gas I give it the worse it gets.  I've checked all hoses MAF sensor, catalytic converter and replaced the fuel filter.  Any suggestions, someone has said that it may be the computer because I did not disconnect the battery first.