My old 600x, which has been running perfectly, has suddenly developed a fault.
I took it to hospital for my partner to use during her stay and I have now brought it home and it will not run for me.
When I plug it in it tells me that the PSU is not connected (but it is) and keeps on switching off. I have checked the PSU and there is power getting to the connector so nothing wrong there.
Can anyone help me please?

Most likely a bad connection at the power jack. Very common problem with laptops (especially if excessive stress is put on the power cable while plugged in). Might be able to just bend the contacts to make a better connection but the jack might need to be re-soldered or replaced.

Thanks I will try that tomorrow with the jack socket.

I ahve tried the plug socket and it seems OK. I have also purchased a replacement PSU and have just plugged in and nothing is happening.
I get no lights at the back of the 600x where it shows if the power is on .
Thinking about the demise I had it in hospital so my partmer could watch films etc while she was recovering from a heart attack. Over the last two days of her being there I noticed the power lights were flickering and not coming on at points and now there is nothing.
Would it be that my trusty old friend has finally died on me? If so any ideas what I can try next please guys?

Take out all removable hardware (RAM, PCMCIA/cardbus-cards, mainbattery, cmos-battery, ultrabaydrive, hdd, tv-out-card, modem/minipci-card... reseat mainprocessorcard, remove the PCMCIA/cardbus-holder from mainboard, try to start only with powersupply, try to start only with battery. Then try to start without keyboard, then without display, then without subboard.

If doesn't work, remove the mainboard and check for any damage (fluids), then check the fuses with a multimeter (fuses are marked as F1, F2...).

Just to let you know the 6oox is alive and kicking.
Turned out to be a duff power supply after all that.

Thanks to all you who helped.