Dead disco 2.....every now and again

Update.....done it again tonight, been driving today fine, popped to shops, jumped back in, nothing, no red led flashing or doing anything, checked battery connections, all ok. Still no power, earth strap connected in from batt to engine to check if its an earth fault, nothing, poked about in fuse box under bonnet, came to life but wouldnt turn over, red led solid, like immobliser had kicked in, locked, eka code input, started fine like nothing had happened

Dash when car wouldnt turn over, lights on but starter wouldn’t engage, 1st time its done this