Quite often it will be faster to reinstall Windows, than to keep fighting the windmills of problems, like RPCRT4.dll... not that simple, no definitely clear answers. By the time you get unused programs uninstalled, you would already have reinstalled the whole OS, with a newly partitioned disk etc. = a somewhat clear table.
It could be a matter of codecs, but who knows. You could uninstall all extra codec packs you have, return to Windows basics. Or, you could pick a restore point from before you remember to have got the problems. That'll take 15 minutes, you might try it.
If you decide to reinstall, or even otherwise, it wouldn't be a bad move to have your disk partitioned in at least two, one C for Windows and crucial programs, the other for your own files - that way you don't risk your own files when you reinstall Windows. Do not name any partitions D, because that may cause trouble with games or something playing CDs or DVDs. But the names of disks can be changed afterwards.
Windows does have problems with partitions. I would recommend AOMEI
http://www.aomeitech.com/aomei-partition-assistant.html or GParted
http://gparted.org/ Since there may be lots of questions, I stop here. Most of the people here know a lot more than I.