Moves in circles and backwards, though will not move forward

The roller brush is not balanced. Check everything inside the head unit. Brush, belt and debris. The belt may have burn marks from the motor shaft or if someone worked on the vacuum cleaner beforehand, this could be the only reason.

That is brobably a bad wiring, that lose contact when you move the hoover forward. The wirings should be checked, here is some schematic:
Wiring Schematic :

Are you getting any error codes? Could be a bad LED sensor on the front bumper. Or a stuck wheel? Take a look at this - https://homesupport.irobot.com/app/answers/detail/a_id/7265/~/the-roomba-800-series-error-messages-chart.

Generally the belt is probably stretched and needs replacing but I have had several that required modifying the height adjustment assembly. Belt should be a bit of a fight to stretch and get the brush block back in properly to maintain resistance. The higher carpet causes the belt to slip and can even cause burn/wear from the motor shaft spinning in one spot. Sometimes people run them and burn through and break the belt. Generally you smell rubber burning if belt is slipping and burning. The height adjustment modification was a last resort and not easy! Not for the average person! Another post tells how to modify but better be handy!

tip unit back to lift brushes off floor and roll forward until over carpet edge. tip back unit to sit flush on carpet and unlock handle so it swings freely. now pull backwards ith finger on spray trigger. that's how it works, not by pushing forwad.

Sounds like either the battery is bad or not being charged properly with subsequent loss of programming.

Blow out the unit with compressed air, particularly around the wheels and under the bumper. Tap the bumper with your hand.

If your Roomba stops and beeps at you, count the beeps AFTER the initial "uh-oh" tone. Then call customer support (1-877-855-8593) for assistance.

Good luck.

Apache Server at www.youtube.com Port 80

Are you sure its not just your belt on the beater of head slipping and needs to be replaced?

on the front of the base there are 3 very small rollers made out of rubber, these are either just dry and won't turn or worn and or damaged,

that is your problem / honest its that simple