repeating blue screen error memory management

we recently update out desktop to Win 7 home premium- after install it seemed to work and boot fine, we then loaded Norton and found that there was not enough memory so we added 2 ram sticks that are compatible with Dell Dimension 4700 Intel Pentium 4 CPU 2.80GHz. Computer seemed to work fine. that last time we are sure it worked was Oct 16th - I synchronized my Ipod via Itunes, removed my songs and updated my calendar. Upon return form a trip the computer would not boot, so say my kids...since then we have spent hours with Norton techs no bugs and Microsoft/Symantec and still cannot get it to boot except in safe mode. I have run multiple test to see if we could find the error but have not had any luck. One blue screen read mem mngmt error 0x00000014 (0x00041790 0xC040204A 0x0000FFFF 0x00000000)
not really sure what to do or where to find help...not super computer savvy Alleto06