2010 original cellular iPad is not charging

If the iPad has not been recharged for many months - the battery may have failed due to deep discharge. It is generally recommended that an unused iPad is recharged every six months to protect the battery from potential damage:

Batteries - Maximizing Performance - Apple

These support pages should help with troubleshooting battery and charging issues:

Charge and monitor the iPad battery - Apple Support

If your iPad won't charge – Apple Support

Troubleshooting generally requires substitution of the Power Adapter and cable for another known-good item. Most models of iPad require a Power Adapter rated at 12W (i.e., 2.4A @5V) or greater to reliably charge. 5W Power Adapters (1.0A @5V) intended for older models of iPhone are inadequate to charge an iPad; if the iPad charges at all, charging will be very slow. Recent models of iPad are supplied with a 20W USB-C Power Adapter.

Some third-party USB-C power adapters (and portable PowerBanks) may not support USB PD (Power Delivery). Power Delivery mutually negotiates the charging voltage; the source, load and cable are all elements involved in the negotiation protocol. Unless the Power Adapter explicitly supports USB PD, it will almost certainly fail to charge the iPad; proprietary charging standards, such as QC (Quick Charge), are not supported.

Many computer USB ports also cannot source sufficient power to charge an iPad. Unless explicitly designed for charging connected devices, computer USB ports are typically limited to 0.5-1A @5V (i.e., 2.5-5.0W).

If you continue to experience difficulties when using an appropriate Power Adapter of 12W or greater, you might be best advised to seek assistance directly from from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad, Power Adapter and cable(s). If your iPad battery has failed, you'll be in the beet possible place to explore your available options:

Genius Bar Reservation and Apple Support Options - Apple

Alternatively, you might consider using Apple's Mail-in repair service for assessment - and if required, replacement of the iPad battery:

iPad Repair & Service – Apple Support (UK)

For practical purposes, in lieu of replacing the battery and returning your own iPad, Apple usually exchange an qualifying iPad for a renewed/refurbished iPad of the same model and specification. The cost of the exchange is the same as would otherwise be charged for battery replacement.

It could just be that the battery has reached the end of its life and will no longer accept a charge or if it was left off the charger for a long time has depleted it's charge to a point that it can no longer accept a charge anymore. Either way, it sounds like a battery replacement would be the only option to get this going again.

That being said, at the age of the iPad, it's not going to be worth putting money into it. There is no way that the hardware in that device is going to support anything more up to date and you're going to find that things are extremely limited as to what you can do on the device. Most of the apps are going to require updating the OS which you won't be able to do because the hardware will not support the updates.

Check the charging port of the iPad with a toothpick or toothbrush in case anything is stuck in it.