Philips MT5000. Spec as follows:
Intel Core 2 Duo Processor E6420 2.13GHz, 1066MHz FSB, 4MB Cache Genuine Windows Vista(TM) Home Premium 2048MB RAM Memory 400GB Hard Drive Dual Layer DVD Re-Writer Drive 256MB ATI Radeon X1550 Graphics 802.11b/g Wireless Network Ready 8-In-1 Media Card Reader

Switch it on - no beeps, monitor with amber light, dead keyboard and mouse.
All fans working - mobo, VGA card, case, PSU.
Have changed:
RAM 2x PC5300 to 2xPC4200 - alsio tried each stick on its own in each of the 2 slots. Brand new from Crucial.com.
Graphics card to a 128Mb PX6600 PCI Express.
Have bought new 300W PSU and installed. Also tried a 430W from other PC.
Have taken battery out and swapped jumper from 1&2 to 2&3 for 30mins.

Have literally tried everything except a new mobo !
Any ideas anyone ?

Its a refurb model and when I first got it it did start for one session then froze and has never restarted.

Has 24 pin PSU connector and 4 pin to the mobo. Have also unplugged all hardware - HDD, DVD.

ok start by putting the original RAM back the way it was. now with the HDD disconnected turn on the computer. does the monitor turn on and if does, does it say "no operating system found".

No the monitor remains on amber. Have also unplugged the DVD rewriter too.

sounds like the mobo could have gone on to mobo heaven.
make sure the extra 4 pin connector is seated all the way.

you can try a different graphics card and you can try your monitor on a different computer if it turns on you now its good. if you get the same problem with a new card and you now the monitor is good I would start looking for a new mobo.

The monitor is good - from other PC which works a treat and have tried new VGA card too.

Do NOT BUY this computer system!!! i bought mine at PC world and the sales assistant told me that it had a 450W power supply. However, 3 months down the road power supply burnt and and burnt my hard drive too. When open up the case there was only a 300W power supply in there!! No wonder it burnt!!

Anyway i got a new hard drive, and an OCZGXS600 600W power supply. that run fine for 3 months too and power supply burnt again!!!

Now on im third power supply and the system just restarts for now reason. Customer service at PC world is bad!!!!!

So KEEP AWAY FROM THIS COMPUTER SYSTEM!!!!

Well I think you might be better off putting this message else where as people come to this site once hte damage is already done after they have bought it mate. SOrry to hear you troubles with the system though.

Raj