I take it since it's blue screening, it's a PC. To squeeze some life out of it, get some compressed air in a can, blow out everything, especially the fan for the CPU. Next, backup your important stuff onto an external flash drive or hard drive. Then reformat the computer, loading Windows from scratch and reload the programs. After installing your virus/malware software of choice, scan your flash drive/external hard drive before moving those files over. That should breathe some more life into that computer for you.

4+ years isn't that old. I have an old 7+ year old MacBook (one of the first original white ones) that I just recently threw a cheap SSD into, maxed out the RAM, reinstalled the OS and I was able to run Photoshop CS5 on it with a 30x40 inch signage file I was working with when I was at BLFC. It impressed me quite a bit with how much the old girl can handle.