Here is a link to a driver I found to work. I don't have any devices to verify that it works, but it removes the exclamation point. I unzipped the file, then unzipped the drivers in there and installed it. I did not use the setup.exe.
I have OptiPlex 990 purchased at the end of 2012 it originally had Windows 7 64-bit I upgraded to Windows 10 64-bit and I am unable to find a driver for the PCI Serial Port. I have found driver for Windows 7, but I'm unable to find it for Windows 10. When I go into the properties for the serial port it gives this information below. Device PCI\VEN_8086&DEV_1C3D&SUBSYS_047E1028&REV_04\3&11583659&0&B3 requires further installation. If anyone can help I would appreciate it Thank You George 
PCI Serial Port for OptiPlex 990 with Windows 10 64 bit