Its true I bought a PC, but ... (I have no idea how to use it)
my text book explaints it with: けれども 〜ということは本当だが、しかし
You can replace with them. 〜けれども／〜ということは本当だが、しかし →パソコンを買ったけれども、使い方が全然わからない。
this "but" seems to lean toward "although" 〜 のに
Quite often used in the construct ~とはいうものの, with a noun before と it's always used in that form.
ものの should be equated to "although" or "despite the fact that..." rather than "but" so that "I bought a PC, but I have no idea how to use it" shold preferably be "Although I bought myself a PC, I have no idea how to use it."