I have this 1984 Hitachi VT35E VCR, it's a real tank and it had a good picture when it still worked.

Some months ago it suddendly stopped working, when i turn it on with the "operate" button, the "tape in" indicator on the eject button stays lit even though there's no tape inside and the carriage is in its correct position to accept a tape, then after a few seconds the machine shuts off.

Also when it still worked the rewind/fast forward buttons often malfunctioned, you often pushed "rew" and the VCR would fast forward instead

What can be wrong? maybe there's some dirty switch?

It might be a bad tape-end sensor. It's been a really long time since I worked on one of those, but I think that may be it. If I remember correctly, when they go bad it'll act like this, but if you press the eject button then insert the tape immediately it'll take it in and load it in a second or two. I think it's the sensor on the right side of the loading carriage, under the gears and motor.

The thing with RW and FF acting funny may be a dirty mode switch under the deck.....It's possible that is responsible for the "Tape-in" indication too, but my money is on the end sensor for that one.

Back in the good old days, I'd often see machines like this, and replace both of these items (or clean the switch rather than replace it) and snap a new set of belts on it, clean it up, and it would be good to go.

If it's the European version of this beast, then yes, the end sensors are your primary problem. Intermittent REW and FF are like the previous poster said - the mode switch, or "mechanical state sensor switch" as it was called by Hitachi.

VT-35A = America, VT-35E = Europe, I presume.