Insufficient memory and heat issues may cause a computer to lock up. Depending on the exact reason behind the problem, an individual can resolve either issue within the operating system or by upgrading system components.
To determine whether or not insufficient memory is the cause of a lock up, open the Task Manager by right clicking on the taskbar and selecting Task Manager. Navigate to the performance tab, and check memory usage. If it seems that the system does not have enough memory, either try to close some applications, or add more RAM to your computer.
Use a heat monitor such as the Open Hardware Monitor to check if your system is overheating. Refer to the manuals of your processor and graphics card to find out their optimal heat values. If Open Hardware Monitor displays high temperature values, buy more powerful fans or thermal paste to improve the cooling of your computer. Alternatively, closing some applications to ease the workload on the system is a temporary solution that helps cool down the system.