Inspiron 7720 doesn't boot sometimes

Hello!

I have quite a situation with my don't-remember-how-much old laptop (>3 years is for sure), which's Inspiron 17R 7720-6167 with dual boot Windows + Ubuntu on two different HDDs.

Not a long time ago, my computer started to not boot sometimes. Not boot means: power button glows all the time, hdds start to spin as I can hear, cpu n all started working, all leds started glowing correctly, but puff, and just... silence. Power button still glows, though, just as a side led for "Power". But it just silently does nothing. No hdds spinning, no "beeps" from BIOS, no glowing of other side led (except for Power one ofc). Oh, and power supply led glows ok too.

But, if I leave it for some time, laptop will likely boot. Diagnostics showed nothing particular: everything is ok, except not having a battery (got a warning for it 1y ago or so, didnt really need a new one) and short self test failure for the main drive. I will list SMART-test result for this drive below.

Other symptoms:

Noticed that Ubuntu sometimes freezes during any IO-heavy operation, such as copying of a lot of files/big files.

Encountered a few errors during copying on external drives, such as unremovable folders or something. E.g. I deleted folder with files, but the folder itself stayed not touched, and gave me 0x80004005 error out of blue next time I tried to delete. Standard Windows error fixing for drives fixed it, though.

Tryed removing memory. Beeps 2 times just as expected. But if I put it back, 4 times out of blue. Ok, I moved to another slot (have one 8gb module), worked ok. Strange.

It's not covered by guarantee, I guess, as I had, afaik, standard 1 year one. That's why I seek for help from you guys.

Thanks!

SMART test for Main HDD that failed short self test in Diagnostics:

HDDScan S.M.A.R.T. Report
Model: WDC WD10JPVT-75A1YT0
Firmware: 01.01A01
Serial: WXS1E32TUJYK
LBA: 1953525168
Report By: HDDScan for Windows version 3.3
Report Date: 7/6/2017 7:35:09 AM

 Num    Attribute Name              Value    Worst     Raw(hex)       Threshold 
 001    Raw Read Error Rate          200      200   0000000000-0629     051
 003    Spin Up Time                 183      178   0000000000-0731     021
 004    Start/Stop Count             093      093   0000000000-1B81     000
 005    Reallocation Sector Count    200      200   0000000000-0000     140
 007    Seek Error Rate              200      200   0000000000-0000     000
 009    Power-On Hours Count         079      079   0000000000-3C37     000
 010    Spin Retry Count             100      100   0000000000-0000     000
 011    Recalibration Retries        100      100   0000000000-0000     000
 012    Device Power Cycle Count     095      095   0000000000-15BB     000
 191    G-sense Rate/Servo tracking  001      001   0000000000-06BE     000
 192    Emergency Retract Count      200      200   0000000000-028B     000
 193    Load/unload Cycle Count      175      175   0000000001-309C     000
 194    HDA Temperature              103      079   44 C                000
 196    Reallocation Event Count     200      200   0000000000-0000     000
 197    Current Pending Errors Count 200      200   0000000000-0001     000
 198    Uncorrectable Errors Count   100      253   0000000000-0000     000
 199    UltraDMA CRC Errors          200      200   0000000000-0000     000
 200    Multi Zone Error Rate        200      200   0000000000-0001     000
 240    Heads Flying Hours           080      080   0000000000-3A70     000
 241    Total Host Writes            200      200   00000F568D-54C8     000
 242    Total Host Reads             200      200   00001308BF-280B     000
 254    G-shock/Free-fall Event Count 200     200   0000000000-0000     000