I have just Upgraded (pretty heavily) my PC. It is now..

ECS PF88 Extreme Hybrid Motherboard
Pentium 4 3.0Ghz with HT Processor
Nvidia 6600LE Graphics card.
512mb DDR2 Ram
40GB HD

When I first built it a few days ago and switched it on it said No Signal on the monitor. Then after a while spontainiously came on and worked superbly. Then yesterday I turned it on and it gave one long beep and said no signal again. Each time I switch it on now it says no signal. However the strange thing is that it responds when I turn the PC on. (No signal is constantly there when PC off, when I turn it on it goes away for 3-4 secs then comes back) Please help me! After spending £370 on all the stuff I am quite upset at the fact it doesn't work.

This sounds like a problem with the video board not being seated properly. Or it could be a loose cable on the monitor. Try making sure the board is seated properly and the cable is tight on both ends.

A 40G HD? That's pretty small by today's standards. Most entry level desktops come wioth 120-160G drive.

By the way, I would say that someone who heavily upgrades their own machine is beyond the Beginner stage. This question would have been better posted in the Computer Hardware forum.

Yes it is quite small but I had a budget and that was the easiest place to save money with out sacrificing performance. Checked all of the above I have a feeling it is the power supply now thanks for your input and apoligies for posting here.

No need to apologize, just offering some advice for the future.