Well. I have just reformatted hard drive and installed windows 7 with updates and relevant software. The battery is defunct so I left it out. No sooner had I had it running for maybe an hour it switched off. Checked the power supply and found it dead. Fortunately I had a spare in the shed. This ran the laptop for another few minutes and this battery died too. Both PSU's were original Toshiba ones for the said laptop. I am loathe to try another until I can spot the cause. The fan is clean and there is no overheating. Thanks for your help.