Gfilui

I just installed Ubuntu 14.04.5 (Desktop LTS, x86) on my Acer Aspire E15 E5-576G-55Y4 laptop and wifi is not working or appear in Network Manager, but Ethernet works fine. How to fix this problem?

ifconfig:

 eth0 Link encap:Ethernet HWaddr d8:c4:97:0f:5b:95 
 inet addr:192.168.1.221 Bcast:192.168.1.255 Mask:255.255.255.0
 inet6 addr: fe80::dac4:97ff:fe0f:5b95/64 Scope:Link
 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
 RX packets:26366 errors:0 dropped:0 overruns:0 frame:0
 TX packets:2802 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1000
 RX bytes:3380631 (3.3 MB) TX bytes:454525 (454.5 KB)

 lo Link encap:Local Loopback 
 inet addr:127.0.0.1 Mask:255.0.0.0
 inet6 addr: ::1/128 Scope:Host
 UP LOOPBACK RUNNING MTU:65536 Metric:1
 RX packets:527 errors:0 dropped:0 overruns:0 frame:0
 TX packets:527 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1
 RX bytes:78183 (78.1 KB) TX bytes:78183 (78.1 KB)

lshw -C network:

 *-network UNCLAIMED 
 description: Network controller
 product: Intel Corporation
 vendor: Intel Corporation
 physical id: 0
 bus info: pci@0000:03:00.0
 version: 10
 width: 64 bits
 clock: 33MHz
 capabilities: pm msi pciexpress bus_master cap_list
 configuration: latency=0
 resources: memory:b4100000-b4101fff
 *-network
 description: Ethernet interface
 product: RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
 vendor: Realtek Semiconductor Co., Ltd.
 physical id: 0.1
 bus info: pci@0000:04:00.1
 logical name: eth0
 version: 12
 serial: d8:c4:97:0f:5b:95
 size: 1Gbit/s
 capacity: 1Gbit/s
 width: 64 bits
 clock: 33MHz
 capabilities: pm msi pciexpress msix vpd bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd 1000bt 1000bt-fd autonegotiation
 configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=2.3LK-NAPI duplex=full firmware=rtl8411-2_0.0.1 07/08/13 ip=192.168.1.221 latency=0 link=yes multicast=yes port=MII speed=1Gbit/s
 resources: irq:127 ioport:3000(size=256) memory:b4004000-b4004fff memory:b4000000-b4003fff

lspci:

00:00.0 Host bridge: Intel Corporation Device 5914 (rev 08)
00:02.0 VGA compatible controller: Intel Corporation Device 5917 (rev 07)
00:14.0 USB controller: Intel Corporation Device 9d2f (rev 21)
00:14.2 Signal processing controller: Intel Corporation Device 9d31 (rev 21)
00:15.0 Signal processing controller: Intel Corporation Device 9d60 (rev 21)
00:16.0 Communication controller: Intel Corporation Device 9d3a (rev 21)
00:17.0 SATA controller: Intel Corporation Device 9d03 (rev 21)
00:1c.0 PCI bridge: Intel Corporation Device 9d10 (rev f1)
00:1d.0 PCI bridge: Intel Corporation Device 9d18 (rev f1)
00:1d.2 PCI bridge: Intel Corporation Device 9d1a (rev f1)
00:1d.3 PCI bridge: Intel Corporation Device 9d1b (rev f1)
00:1f.0 ISA bridge: Intel Corporation Device 9d4e (rev 21)
00:1f.2 Memory controller: Intel Corporation Device 9d21 (rev 21)
00:1f.3 Audio device: Intel Corporation Device 9d71 (rev 21)
00:1f.4 SMBus: Intel Corporation Device 9d23 (rev 21)
01:00.0 3D controller: NVIDIA Corporation Device 1d10 (rev a1)
03:00.0 Network controller: Intel Corporation Device 24fb (rev 10)
04:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. Device 5287 (rev 01)
04:00.1 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 12)

I can't upgrade distr to Ubuntu 18.04 LTS or 16.04 due to compatibility of the OS with various programs

You will need backports to use that wifi card in Ubuntu 14.04

sudo apt-get install build-essential
wget https://mirrors.edge.kernel.org/pub/linux/kernel/projects/backports/stable/v4.14-rc2/backports-4.14-rc2-1.tar.gz
tar -zxvf backports-4.14-rc2-1.tar.gz
cd backports-4.14-rc2-1
make defconfig-wifi
make
sudo make install
cd /lib/firmware
sudo wget https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/iwlwifi-3168-22.ucode

cd backports-4.14-rc2-1
make clean
make defconfig-wifi
make
sudo make install

Anzipex try retarting your network manager. Follow this link for more get help
How to restart WiFi connection?