Slow slow slow windows 8.1

I have HP ProBook 4540 running Windows 8.1 64-bit. My laptop runs ok after a fresh restart for a few minutes. After opening a few applications things start not responding, hanging, crashing. The search facility on Windows Explorer can take 30 minutes to come up with any results. I get runtime errors in C:windows/explorer.exe

It's incredibly slow,

Any suggestions? Thanks