Windows crashes when multiple files are accessed

[Sherri]

I have a client running Windows 98. She often is editing
Excel spreadsheets. When she does, she opening and
closing many spreadsheets at a time, and she says that
often, in the midst of editing them, her computer will
crash, and reboot itself.

Any ideas as to why this is happening?

I've applied all of the available Windows98 updates.

Thank You