YES, the battery or power supply is kinda failing, it wasn't charging, so I removed the battery and it runs only with the power supply, I bought a new battery, but it still doesn't work, so I guess it might be the power supply or something inside ?? Could this be causing the slow response ?
Yes, this can directly relate. It's actually a very common issue. Dell laptops will throttle the CPU to a very slow speed if they do not understand what charger they are plugged into, whether it's the charger's fault, the charging port's fault, or even the motherboard (rare, but across so many Dells, I've seen it on rare occasion). The charger tips are dinky and easily messed up, so it's very commonly that, however the DC jacks also tend to follow.
Go to the BIOS and see what it shows for the charger wattage. If this is the problem, it will say there is an "Unknown" charger plugged in. If so, there's the problem - you will need to try a new charger, and if this doesn't help, a new DC jack. (For the record, I'd recommend enabling charger wattage alerts so that this isn't a surprise.)
If not this, I'd treat it as a non-Dell type of issue and check things like cooling and so on so fourth.
Fortunately, if it comes to the DC jack, that looks to be pretty easy on the 7359 - just unscrew and pop off the bottom cover, and you should see it right there. It comes out with just one small screw. New jacks can be found on eBay and Amazon aplenty for cheap, just be careful with connectors etc. during the process.
Best of luck!