|OK here is something you can try:|
I am thinking that it might be a CPU overheating problem due to clogged up cooling fan.
Open your case and give it a good dusting. If you work carefully you can use a household vacuum cleaner to vacuum all dust and fluff accumulated in the heatsink and fan assembly.
While your are at it give it a good clean inside.
After that check all the cables are fully pushed home where they should be. This includes all power cables, IDE cables and any other.
Once you have done this try booting up.
This works quite often. You may be surprised.
Are you sure that the model is HP Pavilion 525 W. The reason for asking is that I could not find such a model on HPs website. The nearest I found was a HP Pavilion w5251 which is from the HP Pavilion w5200 Desktop PC series.
Here is the link to it:
☺ When everything else fails, read the instructions.