Windows recently (past 3 or 4 days) did a bunch of updates to my W10 PC.
I have 3 separate Arduino IDE 1.8.19 installations (AVR, ESP & SAMD), all in portable mode and suddenly all 3 have started throwing errors whilst starting the IDE. I just tried a completely clean 1.8.19 from the zip archive and that also throws the same errors.
Picking my SAMD portable setup as an example (all 3 throw the same errors), starting arduino.exe throws:
If I click OK, the dialog goes away - but no IDE appears. A second attempt to launch the IDE and:
If I click OK, the dialog goes away - but no IDE appears. A third attempt to launch the IDE and:
A reboot seems to fix the issue temporarily, but I noticed that the next day it's back again.
Anybody else come across this recently?
I do not actively use my 1.8.19 portable setups. Just tested and mine starts as usual.
Win10 home edition.
Have you looked why you possibly might have the "access denied" error?
I'm on W10 Pro - thought it was W10 Home till I just checked...
Just powered on again after lunch and interestingly Java wanted to do an update. I let it update and things seemed to have settled down for now.
Strange. The IDE comes with its own JRE which to my knowledge will not be updated by Windows or Java (e.g. Oracle's Java).
But glad it's sorted (for now).
No problems here but I am using Linux. You can probably load linux on your computer and run either linux or windows whenever you want,
It seems rather random. I have 3 separate IDE setups for AVR, SAMD and ESP32. When the problem occurs, all 3 IDEs are affected.
It seems that a reboot temporarily resolves the issue. As @sterretje mentioned, if the IDE is selfcontained, then I can't figure out why the errors are appearing.
I wondered if it might be W10 blocking a downloaded file from running, or some other security issue that's now happening because of a W10 update.
Strangely, my other W10 PC is behaving.
I haven't see any other reports of this specific problem before, but sometimes we receive reports of sketch compilations failing with mysterious "access is denied" errors. In that case, the cause is usually found to be interference caused by the user's antivirus/security software interfering with the IDE's ability to invoke a compilation command because it is doing a "real time"/"on access" scan on the file. The occurrence of the fault might be timing sensitive, which could cause it to be intermittent.
As an experiment, the next time the problem occurs you can try 
TEMPORARILY disabling the security software/antivirus on your computer for a single attempt to start up Arduino IDE to see if the problem goes away:
- Wait until the next time your system goes into the bad state where Arduino IDE won't start up.
- Disable the security software/antivirus software.
- Attempt to start Arduino IDE again.
- Wait to see whether or not the IDE will start up.
- Immediately enable the security software/antivirus software again.
If the problem doesn't occur with the security software disabled, you will need to adjust the settings of your antivirus to put the appropriate file, folder, or process on the "allow list" so it doesn't interfere with compilation.
Please be cautious about working without an antivirus. This is only about temporarily disabling it for a quick test. If you don't feel comfortable doing that, fine. You can try going straight to configuring the antivirus to not interfere with the Arduino software.