hi, computer info: Dell Optiplex GX520 Intel Pentium 4 CPU 3 Ghz motherboard: Dell.inc. OH8052 Problem: when shutting down my computer a message window appears with the following: the instruction at " 0x00000000" referenced memory at "0x00000000" the memory could not be "read" click OK to terminate the program or click cancel to debug the computer then freezes which ever option I choose and I have to use ctrl-alt-delete to force a shut down. rebooting is normal,desktop loads but none of the icons in the quick launch task bar are functional. I have also noticed that the 'start'button changes from dark to light green each time I try and launch a program, then the freeze-up happens. Safe mode boot up has a similar effect and a forced shut down is required. avg,mbam and super anti spyware fullscans found no malware or spyware. Any help would be appreciated. Thanks in advance, drumma.