Silk Road is itself not an illegal place. You can't criminalize the sale of legal goods, as a general rule.
So the short answer is: No. By buying a thing which you can legally buy, from a place like Silk Road, you are probably not doing anything illegal.
The exceptions would be if:
- cryptography is outlawed in your jurisdiction (in which case any kind of encryption as well as coin mining may also be a no-no)
- masking your location is outlawed in your jurisdiction (Tor obviously cannot be used then)
- buying legal items which may be stolen or otherwise illegally acquired is illegal in your jurisdiction (unlikely, as it isn't that common to criminalize people for something they don't and reasonably CAN'T know about)
Basically, think of it this way: it is not illegal to let gang members blindfold you and drive you to a place the location of which you do not know, so that you can buy stuff from a guy in a trenchcoat with dark glasses, provided that the things he is selling you are not themselves illegal. It is dodgy as hell, and it COULD get you into all sorts of trouble - but that'll likely be from the gang members, the guy with the trenchcoat, or the goods themselves - not from the law.
In this example, TOR is the ride with gang members while blindfolded, SR / the seller is the trenchcoat guy, etc.
If you buy GPUs from a guy with a trenchcoat, but you don't believe that they are stolen and you have no good reason to believe they are stolen, then the only law you are potentially breaking is tax laws, by possessing "money" or a monetary instrument you didn't pay taxes on (crypto) or by wilfully evading sales tax if relevant in your jurisdiction. Bear in mind that "good reason" varies depending on where you are. In some places, if it turned out that an item you bought from a guy in a trenchcoat was stolen, the fact that the transaction took place outside of the normal course of business is viewed as a good clue for you that it probably wasn't legit. That places the weight on you, and thus if the police get a tip, they're going to reclaim the item and return it to its rightful owner. That's relevant in the case of a car, but not likely in the case of a GPU.
As always, I am not a qualified lawyer in your jurisdiction and so anything I say should not be taken as legal advice. But this should hopefully settle that question for you - if the things you're buying aren't illegal, then the act of buying them generally isn't illegal, no matter where you buy them from.