About once in every five starts my computer fails to boot up I then have to switch the power of at the socket (can't switch off at the computer)
Can you please help. Stitcher.

do you get an error message?

where exactly does the boot process stop?

can you get into safemode?

No error message and monitor states no signal.
I can always tell when it's not going to boot up,
there is no BEEP from the computer.
Stitcher

The same is happening to my computer...
have you tried to take out the bios battery, leave it out for while.
it worked for my friends computer but not my own.
can someone help me?

How do you do that. I don't appear to have any battery in my computer,
every time the problem happens or shut off at the socket I have reset clock & date
Stitcher

That is what your CMOS battery looks like

every time the problem happens or shut off at the socket I have reset clock & date

your battery may need replacing then, it is the battery that runs the clock, keeping the date and time.

I dont appear to have a battery as since new I have had to reset time and date every time I shut down at the socket
stitcher

perhaps your batters was always faulty or became un-seated in transit... It's worth a check

I have replaced the battery and still the problem exists, in fact it has deteriated to switching on and off about 8 or 10 times before it starts.
some times it starts and gets as far as system restore and further then the monitor shows no signal and I have to start all overagain.
I have started it in the safe mode but still have the same problem.
Stitcher

When you manage to boot up, click start> rt.click my computer> click properties> advanced> click "settings" under startup ad recovery

in this window, UN-tick the box saying "automatically restart. This should give you a blue screen next time your computer starts... jot down the error code and the message at the top (The error code looks something like 0x0000008D)

Post the error code and message here, this will give us some idea what is causing the error