After restarting N900 it keeps rebooting and not getting past the initial Nokia screen. Have tried to flash but it reboots before it can be done. Any suggestions please

so you've plugged the phone in while holding the U button?

yes. am unable to flash as it goes straight back to reboot

hmm have you tried taking the battery out?

Took battery out, only way to get out of reboot cycle, left out over night hoping it would help but did not. Still same problem occuring. Is there a way to reset without flashing as it does not seem to get anywhere.

Do a full reflash if you can lose all data happily.
Or just reflash the kernel only.

Google will show you how.
That should fix you up.

if it's still in warranty see if Nokia will fix it.

I have just had same issue heres the steps I did.
1:Make sure your battery is fully charged or at least 50% or it will not go into update mode. Even if its rebooting constantly just switch it off and plug in mains charger. It will trickle charge over time.
2:Take out battery and connect the usb cable to both phone and pc.
3:Hold down the U key and then insert battery hopefully this will put it into update mode before it hits the reboot cycle.

Hope this helps. By the way do you know what started the reboot cycle, programmes installed/updated ect.
Im pretty sure miy problems started when I was messing with the SunJava scripts.

maybe a "soft hard reboot" (push on/off butlon for 5sec) will help.
or boot up without a sim installed (if the phone have some sim pin problems)