Why is my laptop blinking power button

This usually happens due to a low voltage on the CMOS battery with many of these laptops - some do not care as MUCH like my E6440 because the Flash ROM and CMOS RAM are power sipping, while others like the E7440 are so sensitive even being .1v below what the board likes may cause an issue and the machine decides to stop booting. With a lot of these weird laptops having different low voltage response tolerances, it is a wildcard situation I tend to tread with caution around unless I know the machine can handle it first hand. An example of this is if I have a laptop with a overly sensitive board like the E7440. As an example, if the A00 board that has issues with batteries at 2.4V (early machines only), while the A01 board can handle it at 2.4V but has a POST error about a low CMOS battery (later production). That tolerance fix may come as a result of a BIOS update, or a hardware revision - usually with HW revisions batteries tend to be cheaper and more accessible then the replacement board which is truly “revised”.

In this case, your best bet to cure this permanently is a new CMOS battery - but for testing the method @oldturkey03 mentioned is best. If you can check it with a multimeter and make sure it’s within 3-2.5V, then I would do it but if not I would probably just replace it just to be safe at that point - especially an older laptop like this. The Lenovo Part# appears to be 04W1642 or 02K7078. If you look at the Lenovo HMM on Page 34, it shows HOW to test the battery as well. Once you have the bottom off, replacement is easy enough you can do it in 20 minutes tops - plus batteries are easy enough to replace it’s usually not worth replacing the board if a revision fixes the issue of CMOS battery sensitivity.