Heh! We must have just been lucky cos we didn't have any problems! ;o)
Moth and Juamei's instructions on the page on this site are pretty well there, and from memory, we WERE either incredibly lucky or access has improved!
My attempt from memory:
There's a layby, right next to the footpath, a few yards up the hill opposite the farm (roughly SY600869). Park there and head along the footpath (ensuring you're on the side of the fence that the cows AREN'T! Not that they'll mind, it's just out of courtesy, like...) You'll eventually come across a stone style in a field wall with "The Hellstone" etched into it, with an arrow pointing up the hill. Go up the hill, et voila! One Hellstone!
And when you get back to the car, go down the hill to the farm, follow the footpath (farm track - unmissable) until you reah the tiny Hampton Down stone circle, for fabulous views on a clear day (if not a slightly overgrown and often underwhelming site itself!)
If you get there using these, let me know and I'll post 'em as fieldnotes..!
Have fun!
Wonder if we could incorporate your visit with our proposed megameet? That'd learn ya... ;o)
G x