We have recently installed an Allen Bradley Programmable Logic Controller in a rack with a power supply. Then we put in cards and pushed the dipswitches to the place were the manual specified per our application. The Allen Bradley is a PLC model 5/40 and we use DH for our remote I/O. Myself and another coworker did all of the programming and it controls pumps and level and temperature things. Upon initial startup everything worked really good, and upon review with the operators, we noted our changes. Well now everytime we sit down to program and I put the PLC in program mode, the PLC stops controlling. How can I control and program at the same time? Would it help if we upgraded the PC from Windows 98 to NT or even 2000? Thank you very much for any assistance.