On one of my PC's (Windows Vista & MSO2007) has started experiencing MAJOR speed issues when opening excel. With all other MS office programmes, it seems to be performing without any difficulty.

Excel files just open really slowly and then when trying to click into a cell, the screen goes white and I get a (not responding) message in the task bar.

Its starting to cause some major frustration - has anyone got any ideas how to improve this?

It might be o problem of excel communication with the printer.
Especially files in page break view stops responding for many seconds, even after they are open.
Try to set your default printer to a virtual printer, like DoPDF printer, and check all installed printers if they have more than 0 documents in queue.
If you notice a significant improve on excel functionality, there you go, you solved the problem.