_wingdi.dll is a direct link library (.dll) file used with a program called Power Series. Its presence on your computer should not of itself indicate any harm. However, it is possible that this file may have been damaged or infected by adware or spyware, or may point to the wrong spot in the Windows registry.
The Windows registry is a database in the operating system that quickly patches operational files into their component parts. Without this database, the program files would be scattered all over your computer. Few operations could run at once, and even then the going would be slow.
Sometimes, over time, the going gets slow regardless. Through no fault of your own, your registry may slow down due to malicious programs, out-of-date entries, and programs that did not uninstall properly.
A regular scan with a registry cleaner will keep a laptop or PC from slowing down and potentially even crashing. You can try a free scan with the ZookaWare PC Cleaner software if you like.