Zcashd not syncing/mining/doing anything

sorry, noob here

ubuntu 16.04
installed zcashd with these instructions: https://github.com/zcash/zcash/wiki/1.0-User-Guide

yesterday, with ./src/zcashd got 4 threads mining, validating transactions and Sol/s's. but today, nothing:

"You are running 4 mining threads.

Since starting this node 43 minutes, 59 seconds ago:
- You have validated 0 transactions!
- You have contributed 0.0000 Sol/s on average to the network solution rate.
- You have completed 0 Equihash solver runs.

Init message: Activating best chain..."

I think it might be something with user rights or something, because once I saw this error message:
"Error opening block database. Do you want to rebuild?"
but have been unable to reproduce that message.

How do I troubleshoot?

Thnaks DocG -- I did this, renamed to blocks.OLD -- still nothing happening. :frowning:

Did you check to stop the process?

Yes.

I wonder, how does one "Rebuild the block database?"

I can see zcashd creates a new "blocks" folder when I start it.

Hi,
Ok.
Stop the process
Run rebuild ( I think this must reset something somewhere in the files structure)
./src/zcashd -rebuild
Then wait 5 mins.
Then stop the process
Then rename the folder and carry on as per the first lot of instructions.

i get:
zcashd: main.cpp:2043: bool ConnectBlock(const CBlock&, CValidationState&, CBlockIndex*, CCoinsViewCache&, bool): Assertion `hashPrevBlock == view.GetBestBlock()' failed.

Hi,
Ok.
Stop the process
Put the old (your first) blocks folder back as it was.
Run rebuild
./src/zcashd -rebuild
Then wait 5 mins.
Then stop the process
Then rename the folder and carry on as per the first lot of instructions.

DocG, I really appreciate the help! However, unfortunately, still does not work ...

So I renamed the first blocks folder back to blocks, ran -rebuild for 5 min and still get:

"You are running 4 mining threads.

Since starting this node 20 minutes, 1 seconds ago:
- You have validated 0 transactions!
- You have contributed 0.0000 Sol/s on average to the network solution rate.
- You have completed 0 Equihash solver runs."