Well, like i said, i had the exact same problem with a laptop last week - power light on, but nothing happening.
Once a good, working PSU was used, everything worked fine.
If the problem is not with memory (which i cant see how it would be), is apparently not the battery or PSU, then without getting my hands on the machine to have a look, there's not much else i can suggest, apart from telling you to take it to a PC repair place and them to have a look.
If the machine is a decent age, i'd be more inclined to tell you to take your cash and get a new one - you can get a decent laptop for �250 - �300 nowadays.
Seeing as your machine is out of warranty, you will have to pay to get it repaired - and with repairs costing about the same, if not more, than a new laptop, common sense will prevail (i hope!)