Weird behavior from 2011 iMac, is it dying?

i purchased used 21.5" imac on summer wife. in need of desktop, , cheap on craigslist. i've been noticing weird behavior on past few weeks. started imac reporting there no boot device randomly couple of weeks ago. thought maybe hdd had died, able use recovery mode , disk utility erase drive , reinstall macos. ran diagnostic on drive , reported fine. wrote off freak occurrence , used excuse install high sierra cleanly. thought going smoothly, noticed wifi started randomly dropping. @ 1 point, though wifi enabled, couldn't see available hotspots. plugging in ethernet cord didn't help. didn't detect connection. tried resetting pram last night, , internet issues seemed resolve itself. morning though noticed internet speed slowed crawl on imac, though fine on other devices on network.

issue i've noticed strange behavior random applications. lot of apps seem hang , require me force quit , restart. lot of laggy/slow response when trying use various apps.

i'm sorry being bit vague, it's difficult pinpoint where/what issue is. did run apple hardware test, , came out clear. of these symptoms sound because of hardware failure? know system bit on old side, , don't mind replacing if needed. don't want write off loss though unless i'm confident it's hardware issue can't fixed.

i've considered taking apple, i'm not sure they'd able do. wouldn't want invest money fixing anyway.

 

sounds dying hdd replace ssd advice.

 

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